Matt Williams, Author at Universe Today

October 12, 2016November 5, 2016 by Matt Williams

A New Dwarf Planet Joins The Solar System Family

Based on data obtained by the Dark Energy Survey (DES), a team of scientists have obtained evidence of another TNO beyond Pluto. Credit: ESO/L. Calçada/Nick Risinger

The Kuiper Belt has been an endless source of discoveries over the course of the past decade. Starting with the dwarf planet Eris, which was first observed by a Palomar Observatory survey led by Mike Brown in 2003, many interesting Kuiper Belt Objects (KBOs) have been discovered, some of which are comparable in size to Pluto.

And according to a new report from the IAU Minor Planet Center, yet another body has been discovered beyond the orbit of Pluto. Officially designated as 2014 UZ224, this body is located about 14 billion km (90 AUs, or 8.5 billion miles) from the Sun. This dwarf planet is not only the latest member of the our Solar family, it is also the second-farthest body from our Sun with a stable orbit.

The discovery was made by David Gerdes, a professor of astrophysics at the University of Michigan, and various colleagues associated with at the Dark Energy Survey (DES) – a project which relies on the Cerro Tololo Inter-American Observatory in Chile. In the past, Gerdes’ research has focused on the detection of dark energy and the expansion of the Universe.

The DECam instrument, . Credit: noao.edu — *The DECam instrument, shown before it was inserted into the Blanco telescope at the Cerro Tololo Observatory. Credit: noao.edu*

Towards this end, DES has spent the past five years surveying roughly one-eighth of the sky using the Dark Energy Camera (DECam), a 570-Megapixel camera mounted on the Victor M. Blanco telescope at Cerro Tololo. This instrument was commissioned by the US. Dept of Energy to conduct surveys of distant galaxies, and Dr. Gerdes had a hand in creating.

Not surprisingly, this same technology has also allowed for discoveries to be made at the edge of the Solar System. Two years ago, this is precisely what Gerdes challenged a group of undergraduate students to do (as part of a summer project). These students examined images taken by DES between 2013-2016 for indications of moving objects. Since that time, the analysis team has grown to include senior scientists, postdocs, graduate and undergraduate students.

Whereas distant stars and galaxies would appear stationary in these images, distant TNOs showed up in different places over time – hence why are called “transients”. As Dr. Gerdes explains in his 2014 UZ224 Fact Sheet, which is available through his University of Michigan homepage:

“To identify transients, we used a technique known as “difference imaging”. When we take a new image, we subtract from it an image of the same area of the sky taken on a different night. Objects that don’t change disappear in this subtraction, and we’re left with only the transients… This process yields millions of transients, but only about 0.1% of them turn out to be distant minor planets. To find them, we must “connect the dots” and determine which transients are actually the same thing in different positions on different nights. There are many dots and MANY more possible ways to connect them.”

*Images of 2014 UZ224, shown on three slides obtained by the DECam. Credit: David Gerdes/DES/University of Michigan*

This was a difficult process. In addition to needing thousands of computers at Fermilab to process the hundreds of terabytes of data, the team had to write special programs to do it. Gerdes and his colleagues also relied on help from Professors Masao Sako and Gary Bernstein of the University of Pennsylvania, who contributed the key breakthroughs that allowed them to perform difference imaging over the entire survey area.

In the end, dozens of new Trans-Neptunian Objects (TNOs) were discovered, one of which was 2014 UZ224. According to their observations, its diameter could be anywhere from 350 to 1200 km, and it takes 1,136 years to complete a single orbit of our Sun. For the sake of perspective, Pluto is 2370 km in diameter, and has an orbital period of 248 years.

Stephanie Hamilton, a graduate student at the University of Michigan, was personally involved with the project. Her role was to determine the size of 2014 UZ224, which was difficult from initial observations alone. As she told Universe Today via email:

“The object’s brightness in visible light alone depends both on its size and how reflective it is, so you can’t uniquely determine one of those properties without assuming a value for the other. Fortunately there’s a solution to that problem – the heat the object emits is also proportional to its size, so obtaining a thermal measurement in addition to the optical measurements means we would then be able to calculate the object’s size and albedo (reflectance) without having to assume one or the other.

“We were able to obtain an image of our object at a thermal wavelength using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. I am working on combining all of our data together to determine the size and albedo, and we expect to submit a paper on our results around mid-November or so.”

Artistic rendering shows the distant view from theoretical Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)

But as with all things related to “dwarf planets”, there has been some disagreement over this discovery. Given the dimensions of the object, there are some who question whether or not the label applies. But as Gerdes indicates on the Fact Sheet, this body fits most of the prerequisites:

“According to the official IAU guidelines, a dwarf planet must satisfy four criteria. It must a) orbit the sun (check!), b) not be a satellite (check!) c) not have cleared the neighborhood around its orbit (check!) and d) have enough mass to be round. It’s this last item that’s uncertain, and the only way for sure is to get a picture that’s detailed enough to actually see its shape. Nevertheless, an object over 400 km in diameter is likely to be round.”

Gerdes and his team expect to be busy, authoring the paper that will detail their findings, using the ALMA array to get more assessments of 2014 UZ224 size, and sifting through the data to look for more objects in the Kuiper Belt. This includes the fabled Planet 9, which astronomers have been seeking out for years.

Given its distance from the Sun, 2014 UZ224’s orbit would not be influenced by the presence of Planet 9, and is therefore of no help. However, Gerdes is optimistic that the evidence of this massive body is there in the data. Given time, and a lot of data-processing, they just might find it! In the meantime, this newly discovered object is likely to be the focal point of a lot of fascinating research.

“It’s an interesting object in its own right – distant objects like this are ‘cosmic leftovers’ from the primordial disk that gave birth to the solar system,” writes Gerdes. “By studying them and learning more about their distribution, orbital characteristics, sizes, and surface properties, we can learn more about the processes that gave birth to the solar system and ultimately to us.”

Further Reading: 2014 UZ224 Fact Sheet (University of Michigan)

October 12, 2016November 5, 2016 by Matt Williams

Turns out Proxima Centauri is Strikingly Similar to our Sun

Artist's depiction of the interior of a low-mass star, such as the one seen in an X-ray image from Chandra in the inset. Credit: NASA/CXC/M.Weiss

In August of 2016, the European Southern Observatory announced that the nearest star to our own – Proxima Centauri – had an exoplanet. Since that time, considerable attention has been focused on this world (Proxima b) in the hopes of determining just how “Earth-like” it really is. Despite all indications of it being terrestrial and similar in mass to Earth, there are some lingering doubts about its ability to support life.

This is largely due to the fact that Proxima b orbits a red dwarf. Typically, these low mass, low temperature, slow fusion stars are not known for being as bright and warm as our Sun. However, a new study produced by researchers at the Harvard Smithsonian Center for Astrophysics (CfA) has indicated that Proxima Centauri might be more like our star than we thought.

For instance, our Sun has what is known as a “Solar Cycle“, an 11-year period in which it experiences changes in the levels of radiation it emits. This cycle is driven by changes in the Sun’s own magnetic field, and corresponds to the appearance of Sunspots on its surface. During a “solar minimum”, the Sun’s surface is clear of spots, while at a solar maximum, one hundred sunspots can appear on an area the size of 1% the Sun’s surface area.

This image is a composite of 25 separate images spanning the period of April 16, 2012, to April 15, 2013. It uses the SDO AIA wavelength of 171 angstroms and reveals the zones on the sun where active regions are most common during this part of the solar cycle. Credit: NASA/SDO/AIA/S. Wiessinger — *Composite of 25 separate images spanning the period of April 16, 2012, to April 15, 2013, revealing active regions during this part of the Solar Cycle.* *Credit: NASA/SDO/AIA/S. Wiessinger*

For the sake of their research, the Harvard Smithsonian team examined Proxima Centauri over the course of several years to see if it too had a cycle. As they explain in their research paper, titled “Optical, UV, and X-Ray Evidence for a 7-Year Stellar Cycle in Proxima Centauri” they relied on several years worth optical, UV, and X-ray observations made of the star.

This included 15 years of visual data and 3 years of infrared data from the All Sky Automated Survey (ASAS), 4 years of x-ray and UV data from the Swift x-ray telescope (XRT), and 22 years worth of x-ray observations taken by the Advanced Satellite for Cosmology and Astrophysics (ASCA), the XXM-Newton mission and the Chandra X-ray Observatory.

What they found was that Proxima Centauri does indeed have a cycle that involves changes in its minimum and maximum amount of emitting radiation, which corresponds to “starspots” on its surface. As Dr. Wargelin told Universe Today via email:

“The optical/ASAS data showed a nice 7-year cycle, as well as an 83-day rotation period. When we broke down that data by year we saw the period vary from around 77 to 90 days. We interpret that as ‘differential rotation’ like that found on the Sun. The rotation rate differs at different latitudes; on the Sun it’s around 35 days at the poles and 24.5 at the equator. The “average” rotation is usually given as 27.3 days.”

In essence, Proxima Centauri has its own cycle, but one that is a lot more dramatic than our Sun’s. Besides lasting 7 years from peak to peak, it involves spots covering over 20% of its surface at one time. These spots are apparently much bigger than the ones we regularly observe on our Sun as well.

X-Ray image of Proxima Centauri. Image credit: Chandra — *An X-Ray image of Proxima Centauri. Credit: Chandra/Harvard/NASA*

This was surprising, given that Proxima’s interior is very different from our Sun’s. Because of its low mass, the interior of Proxima Centauri is convective, where material in the core is transferred outward. In contrast, only the outer layer of our Sun undergoes convection while the core remains relatively still. This means that, unlike our Sun, energy is transferred to the surface through physical movement, and not radiative processes.

While these findings cannot tell us anything directly about whether or not Proxima b might be habitable, the existence of this solar cycle is an interesting find that might be leading in that general direction. As Dr. Wargelin explained:

“Magnetic fields are what drive high energy emission (UV and X rays) and stellar winds (like the solar wind) in solar-type and smaller stars, AND a stellar cycle (if it has one). That X-ray/UV emission and stellar wind can ionize/evaporate/strip the atmosphere of close-in planets, particularly if the planet doesn’t have a protective magnetic field of its own.

“Therefore….. a necessary but not sufficient requirement for understanding (i.e., modeling) the evolution of a planet’s atmosphere is understanding the magnetic field of the host star. If you don’t understand why a star has a cycle (and standard theory says fully convective stars like Proxima can NOT have cycles) then you don’t understand its magnetic field.”

As always, further observations and research will be necessary before we can fully understand Proxima Centauri, and whether or not any planets that orbit it could support life. But then again, we’ve only known about Proxima b for a short time, and the rate at which we are learning new things about it is quite impressive!

Further Reading: CfA, arXiv

October 11, 2016November 5, 2016 by Matt Williams

X-Rays Are Coming From The Dark Side of Venus

On June 5th, 2012, the NASA/JAXA Hinode mission captured these stunning views of the transit of Venus. Credit: JAXA/NASA/Lockheed Martin

Venus and Mercury have been observed transiting the Sun many times over the past few centuries. When these planets are seen passing between the Sun and the Earth, opportunities exist for some great viewing, not to mention serious research. And whereas Mercury makes transits with greater frequency (three times since 2000), a transit of Venus is something of a rare treat.

In June of 2012, Venus made its most recent transit – an event which will not happen again until 2117. Luckily, during this latest event, scientists made some very interesting observations which revealed X-ray and ultraviolet emissions coming from the dark side of Venus. This finding could tell us much about Venus’ magnetic environment, and also help in the study of exoplanets as well.

For the sake of their study (titled “X-raying the Dark Side of Venus“) the team of scientists – led by Masoud Afshari of the University of Palermo and the National Institute of Astrophysics (INAF) – examined data obtained by the x-ray telescope aboard the Hinode (Solar-B) mission, which had been used to observe the Sun and Venus during the 2012 transit.

Artist's impression of the Hinode (Solar-B) spacecraft in orbit. Credit: NASA/GSFC/C. Meaney — *Artist’s impression of the Hinode (Solar-B) spacecraft in orbit. Credit: NASA/GSFC/C. Meaney*

In a previous study, scientists from the University of Palermo used this data to get truly accurate estimates of Venus’ diameter in the X-ray band. What they observed was that in the visible, UV, and soft X-ray bands, Venus’ optical radius (taking into account its atmosphere) was 80 km larger than its solid body radius. But when observing it in the extreme ultraviolet (EUV) and soft X-ray band, the radius increased by another 70 km.

To determine the cause of this, Afshari and his team combined updated information from Hinode’s x-ray telescope with data obtained by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO). From this, they concluded that the EUV and X-ray emissions were not the result of a fault within the telescope, and were in fact coming from the dark side of Venus itself.

They also compared the data to observations made by the Chandra X-ray Observatory of Venus in 2001 and again in 2006-7m which showed similar emissions coming from the sunlit side of Venus. In all cases, it seemed clear that Venus had unexplained source of non-visible light coming from its atmosphere, a phenomena which could not be chalked up to scattering caused by the instruments themselves.

Comparing all these observations, the team came up with an interesting conclusion. As they state in their study:

“The effect we are observing could be due to scattering or re-emission occurring in the shadow or wake of Venus. One possibility is due to the very long magnetotail of Venus, ablated by the solar wind and known to reach Earth’s orbit… The emission we observe would be the reemitted radiation integrated along the magnetotail.”

On June 5-6 2012, NASA's Solar Dynamics Observatory, or SDO, collected images of one of the rarest predictable solar events: the transit of Venus across the face of the sun. This event happens in pairs eight years apart that are separated from each other by 105 or 121 years. The last transit was in 2004 and the next will not happen until 2117. Credit: NASA/SDO, AIA — *Collected images of Venus 2012 transit of the Sun, taken in June of 2012 by NASA’s Solar Dynamics Observatory (SDO). Credit: NASA/SDO, AIA*

In other words, they postulate that the radiation observed emanating from Venus could be due to solar radiation interacting with Venus’ magnetic field and being scattered along its tail. This would explain why from various studies, the radiation appeared to be coming from Venus’ itself, thus extending and adding optical thickness to its atmosphere.

If true, this finding would not only help us to learn more about Venus’ magnetic environment and assist our exploration of the planet, it would also improve our understanding of exoplanets. For example, many Jupiter-sized planets have been observed orbiting close to their suns (i.e. “Hot Jupiters“). By studying their tails, astronomers may come to learn much about these planets’ magnetic fields (and whether or not they have one).

Afshari and his colleagues hope to conduct future studies to learn more about this phenomenon. And as more exoplanet-hunting missions (like TESS and the James Webb Telescope) get underway, these newfound observations of Venus will likely be put to good use – determining the magnetic environment of distant planets.

Further Reading: The Astronomical Journal

October 10, 2016October 10, 2016 by Matt Williams

What was Sputnik One?

Photograph of a Russian technician putting the finishing touches on Sputnik 1, humanity's first artificial satellite. Credit: NASA/Asif A. Siddiqi

Today, people take it for granted that they live in a world that isn’t threatened with imminent nuclear annihilation. A little more than half a century ago, that was the kind of world people lived in, where the United States and Soviet Union were locked in a constant game of one-upmanship that revolved around the development of nuclear weapons.

At the same time, this competition extended to include sports, politics, and the race to reach space. And on October 4th, 1957, the Russians were the first to accomplish this goal with the launch of Sputnik-1, an unmanned research and communications satellite whose appearance ignited the “Space Race” and forever altered the course of history.

Background:

During the early 1950s, the Russians had conducted extensive orbital research using rockets. However, these efforts were limited by the fact that conventional rockets could only achieve orbit for a maximum of a few minutes before falling back to Earth. The next step seemed obvious: placing a research satellite into space that could maintain its orbit and therefore conduct scientific research for an extended period of time.

A "Semyorka" rocket, part of the Soviet R7 rocket family. Credit: Wikipedia Commons/Sergei Arssenev — *Sputnik 1 was launched aboard a “Semyorka” rocket, part of the Soviet R7 rocket family. Credit: Wikipedia Commons/Sergei Arssenev*

Beginning in March of 1954, Russia’s three top scientists – Mstislav Keldysh, Sergei Korolev and Mikhail Tikhonravov – began discussing the idea of creating an artificial satellite that could be placed into orbit. According to Tikhonravov, such a move would be the next necessary step in the development of rocket technology.

Their efforts received a boost when, on July 29th, 1955, U.S. President Dwight D. Eisinhower announced the US’ intent to launch an artificial satellite during the International Geophysical Year (IGY) – an international scientific project that lasted from July 1st, 1957, to December 31st, 1958.

Because of this, the Soviet Politburo approved of the plans for an artificial satellites and aimed for a launch date that would take place before the beginning of the IGY. The project was approve and the task of creating it was divided between various ministries and the USSR Academy of Sciences.

Keldysh was given control of a commission to oversee develop the “automatic laboratory” aboard the satellite, Tikhonravov and his team of engineers would be responsible for designing the satellite, and Korolev – as head of the Ministry of Defense Industry’s primary design bureau (OKB-1) – would be responsible for building it.

*The Sputnik spacecraft stunned the world when it was launched into orbit on Oct. 4th, 1954. Credit: NASA*

Design and Construction:

Initially, the Soviet plan for an satellite (known as Object D) was planned to be completed in 1957–58, and called for the creation of a spacecraft that would have a mass of 1,000 – 1,400 kg (2,200 – 3,100 lb) and would carry 200 – 300 kg (440 – 660 lb) of scientific instruments.

In terms of tasks, the mission would seek to measure the density of the atmosphere and its ion composition, solar wind, the Earth’s magnetic field, and cosmic rays (largely for the sake of future missions). A system of ground stations was also called for in order to collect data transmitted from the satellite, as well as observe its orbit and transmit commands.

By the end of 1956, it had become clear that the specifications called for were too ambitious to be accomplished within the established time frame. Fearing the US would launch a satellite before the USSR, Korolev and the OKB-1 suggested that a simpler, lighter satellite could be launched in April-May 1957, before the IGY began.

This satellite would weight about 100 kg (220 lbs) and would forgo heavy scientific instruments in favor of a simple radio transmitter. On February 15th, 1957, the Council of Ministers of the USSR approved this simple satellite, designated “Prosteyshiy Sputnik” – Russian for “Simplest Satellite” – (aka. Object PS), and made arrangements to launch two versions (PS-1 and PS-2) using R-7 rockets.

*Exploded view of the Sputnik 1 satellite. Credit: NASA*

Launch and Mission:

On October 4th, at 19:28:34 hours Greenwich Mean Time, Sputnik-1 was launched into space from the Baikonur Cosmodrome. The satellite orbited the Earth for three months and emitting radio signals which were monitored by amateur radio operators throughout the world. The signals continued for 22 days until the transmitter batteries ran out on October 26th, 1957.

Before finally burning up during reentry on January 4th, 1958, the satellite traveled a total of about 60 million km (37.28 million mi) and completed 1,440 orbits around the Earth. Sputnik-1 also helped to identify the density of the atmosphere’s upper layer, provided data on radio-signal distribution in the ionosphere, and allowed for the first opportunity for meteoroid detection.

Impact:

Apart from its value as a technological first, Sputnik also had the effect of expediting both Soviet and American efforts to explore space. News of the launch triggered a great deal of fear in the United States, as many worried that Sputnik could represent a threat to national security, not to mention America’s technological leadership.

As a result, Congress urged then-President Dwight D. Eisenhower to take immediate action, which resulted in the signing of the National Aeronautics and Space Act on July 29th, 1958, officially establishing NASA. Immediately, NASA became dedicated to researching hypersonic flight and taking the necessary steps towards creating crewed spacecraft.

*Yury Gagarin before a space flight aboard the Vostok spacecraft. April 12, 1961 Credit: RIA Novosti*

The Soviets did the same, taking drastic steps towards the creation of rockets and crew capsules as part of the Vostok Program. This would culminate in the first man being launched into orbit space – cosmonaut Yuri Gagarin – on April 12th, 1961. The pace of this competition would continue until July 20th, 1969, when the US made the historic first of landing astronauts on the Moon.

Decades later, Sputnik-1 is still viewed as a groundbreaking achievement. Despite its diminutive size and simplicity, its launch was a major breakthrough for the Soviets, and caused no shortage of fear and consternation in the west. In many ways, we are lucky to be living in an age where cooperation has taken the place of competition. Today, such breakthroughs are the result of a world coming together, and not enmity between nations.

We have written many articles about the satellites and Space Age here at Universe Today. Here’s Who was the First Dog to go into Space?, Who was the First Monkey to go into Space?, Who was the first Man to go into Space?, Who was the First Woman to go into Space? and Who Are The Most Famous Astronauts?

If you’d like more information on the Sputnik mission, here’s a link to NASA’s Solar System Exploration Guide on Sputnik, and here’s the homepage for NASA History: Sputnik.

We’ve recorded an episode of Astronomy Cast all about the History of Astronomy. Listen here, Episode 187: History of Astronomy, Part 5: The 20th Century.

Sources:

October 7, 2016November 5, 2016 by Matt Williams

Is Proxima Centauri b Basically Kevin Costner’s Waterworld?

Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)

The discovery of an exoplanet candidate orbiting around nearby Proxima Centauri has certainly been exciting news. In addition to being the closest exoplanet to our Solar System yet discovered, all indications point to it being terrestrial and located within the stars’ circumstellar habitable zone. However, this announcement contained its share of bad news as well.

For one, the team behind the discovery indicated that given the nature of its orbit around Proxima Centauri, the planet likely in terms of how much water it actually had on its surface. But a recent research study by scientists from the University of Marseilles and the Carl Sagan Institute may contradict this assessment. According to their study, the exoplanet’s mass may consist of up to 50% water – making it an “ocean planet”.

According to the findings of the Pale Red Dot team, Proxima Centauri b orbits its star at an estimated distance of 7 million kilometers (4.35 million mi) – only 5% of the Earth’s distance from the Sun. It also orbits Proxima Centauri with an orbital period of 11 days, and either has a synchronous rotation, or a 3:2 orbital resonance (i.e. three rotations for every two orbits).

*Artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. Kornmesser*

Because of this, liquid water is likely to be confined to either the sun-facing side of the planet (in the case of a synchronous rotation), or in its tropical zone (in the case of a 3:2 resonance). In addition, the radiation Proxima b receives from its red dwarf star would be significantly higher than what we are used to here on Earth.

However, according to a study led by Bastien Brugger of the Astrophysics Laboratory at the University of Marseilles, Proxima b may be wetter than we previously thought. For the sake of their study, titled “Possible Internal Structures and Compositions of Proxima Centauri b” (which was accepted for publication in The Astrophysical Journal Letters), the research team used internal structure models to compute the radius and mass of Proxima b.

Their models were based on the assumptions that Proxima b is both a terrestrial planet (i.e. composed of rocky material and minerals) and did not have a massive atmosphere. Based on these assumptions, and mass estimates produced by the Pale Red Dot survey (~1.3 Earth masses), they concluded that Proxima b has a radius that is between 0.94 and 1.4 times that of Earth, and a mass that is roughly 1.1 to 1.46 times that of Earth.

As Brugger told Universe Today via email:

“We listed all compositions that Proxima b could have, and ran the model for each of them (that makes about 5000 simulations), giving us each time the corresponding planet radius. We finally excluded all the results that were not compatible with a planetary body, basing on the formation conditions of our solar system (since we do not know these conditions for the Proxima Centauri system). And thus, we obtained a range of possible planet radii for Proxima b, going from 0.94 to 1.40 times the radius of the Earth.”

Goldilocks Zone — *Tidally-locked planets like Gliese 581 g (artist’s impression) are likely to be “eyeball” worlds, with a warm-water ocean on the sun-facing side surrounded by ice. Credit: Lynette Cook/NSF*

This range in size allows for some very different planetary compositions. At the lower end, being slightly smaller but a bit more massive than Earth, Proxima b would likely be a Mercury-like planet with a 65% core mass fraction. However, at the higher end of the radii and mass estimates, Proxima b would likely be half water by mass.

“If the radius is 0.94 Earth radii, then Proxima b is fully rocky with a huge metallic core (like Mercury in the solar system),” said Brugger. “On the opposite, Proxima b can reach a radius of 1.40 only if it harbors a massive amount of water (50% of the total planet mass), and in this case it would be an ocean planet, with a 200 km deep liquid ocean! Below that, the pressure is so high that the water would turn into ice, forming a ~3000 km thick ice layer (Under which there would be a core made of rocks).”

In other words, Proxima b could be an “eyeball planet”, where the sun-facing side has a liquid ocean surface, while the dark side is covered in frozen ice. Recent studies have suggested that this may be the case with planet’s that orbit within the habitable zones of red dwarf stars, where tidal-locking ensures that only one side gets the heat necessary to maintain liquid water on the surface.

On the other hand, if it has an orbital resonance of 3:2, its likely to have a double-eyeball pattern – with liquid oceans in both the eastern and western hemispheres – while remaining frozen at the terminators and poles. However, if the lower estimates should be true, then Proxima b is likely to be a rocky, dense planet where liquid water is rare on one side, and frozen on the other.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO — *Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. New research suggest the planet may be more watery than previously thought. Credit: ESO*

But perhaps the most interesting aspect of the the research is that it offers a glimpse into the likelihood of Proxima b being habitable. Ever since its discovery, the question of whether or not the planet can support life has remained contentious. But as Brugger explained:

“The interesting part is that all the cases we considered are compatible with a habitable planet. So if the planet radius is finally measured (in some months or years), two cases are possible: either (i) the measurement lies within the 0.94-1.40 range and we will be able to give the exact composition of the planet (and not only a range of possibilities), or (ii) the measured radius is out of this range, and we will know that the planet is not habitable. The case where Proxima b is an ocean planet is particularly interesting, because this kind of planet does not need an atmosphere of oxygen and nitrogen (like on the Earth) to harbor life, since it can develop in its huge ocean.”

But of course, these scenarios are based on the assumption that Proxima b has a lot in common with the planets of our own Solar System. It’s also based on the assumption that the planet is indeed about 1.3 Earth masses. Until the planet can be observed making a transit of Proxima Centauri, astronomers won’t know for sure how massive it is.

Ultimately, we’re still a long ways away from determining Proxima b’s exact size, composition, and surface features – to say nothing about whether or not it can actually support life. Nevertheless, research like this is beneficial in that it helps us to come up with constrains on what kind of planetary conditions could exist there.

And who knows? Someday, we may be able to send probes or crewed missions to the planet, and perhaps they will beam back images of sentient beings navigating vast oceans, looking for some fabled parcel of land they heard about? God I hope not! Once was more than enough!

Further Reading: arXiv

October 6, 2016October 7, 2016 by Matt Williams

What is Galactic Evolution?

Whirlpool Galaxy M51 (NGC 5194). Credit: Hubble Heritage Team (STScI/AURA) N. Scoville (Caltech)

On a clear night, you can make out the band of the Milky Way in the night sky. For millennia, astronomers looked upon it in awe, slowly coming to the realization that our Sun was merely one of billions of stars in the galaxy. Over time, as our instruments and methods improved, we came to realize that the Milky Way itself was merely one of billions of galaxies that make up the Universe.

Thanks to the discovery of Relativity and the speed of light, we have also come to understand that when we look through space, we are also looking back in time. By seeing an object 1 billion light-years away, we are also seeing how that object looked 1 billion years ago. This “time machine” effect has allowed astronomers to study how galaxies came to be (i.e. galactic evolution).

The process in which galaxies form and evolve is characterized by steady growth over time, which began shortly after the Big Bang. This process, and the eventual fate of galaxies, remain the subject of intense fascination, and is still fraught with its share of mysteries.

Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. The goal of the Frontier Fields is to peer back further than the Hubble Ultra Deep Field and get a wealth of images of galaxies as they existed in the first several hundred million years after the Big Bang. Note that the unit of time is not linear in this illustration. Illustration Credit: NASA and A. Feild (STScI) — *Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)*

Galaxy Formation:

The current scientific consensus is that all matter in the Universe was created roughly 13.8 billion years ago during an event known as the Big Bang. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding, and the Universe as we know it began.

After rapidly expanding and cooling, all matter was almost uniform in distribution. Over the course of the several billion years that followed, the slightly denser regions of the Universe began to become gravitationally attracted to each other. They therefore grew even denser, forming gas clouds and large clumps of matter.

These clumps became primordial galaxies, as the clouds of hydrogen gas within the proto-galaxies underwent gravitational collapse to become the first stars. Some of these early objects were small, and became tiny dwarf galaxies, while others were much larger and became the familiar spiral shapes, like our own Milky Way.

Galactic Mergers:

Once formed, these galaxies evolved together in larger galactic structures called groups, clusters and superclusters. Over time, galaxies were attracted to one another by the force of their gravity, and collided together in a series of mergers. The outcome of these mergers depends on the mass of the galaxies in the collision.

Small galaxies are torn apart by larger galaxies and added to the mass of larger galaxies. Our own Milky Way recently devoured a few dwarf galaxies, turning them into streams of stars that orbit the galactic core. But when large galaxies of similar size come together, they become giant elliptical galaxies.

When this happens, the delicate spiral structure is lost, and the merged galaxies become large and elliptical. Elliptical galaxies are some of the largest galaxies ever observed. Another consequence of these mergers is that the supermassive black holes (SMBH) at their centers become even larger.

Not all mergers will result in elliptical galaxies, mind you. But all mergers result in a change in the structure of the merged galaxies. For example, it is believed that the Milky Way is experiencing a minor merger event with the nearby Magellanic Clouds; and in recent years, it has been determined that the Canis Major dwarf galaxy has merged with our own.

While mergers are seen as violent events, actual collisions are not expected to happen between star systems, given the vast distances between stars. However, mergers can result in gravitational shock waves, which are capable of triggering the formation of new stars. This is what is predicted to happen when our own Milky Way galaxy merges with the Andromeda galaxy in about 4 billion years time.

Galactic Death:

Ultimately, galaxies cease forming stars once they deplete their supply of cold gas and dust. As the supply runs out, star forming slows over the course of billions of years until it ceases entirely. However, ongoing mergers will ensure that fresh stars, gas and dust are deposited in older galaxies, thus prolonging their lives.

At present, it is believed that our galaxy has used up most of its hydrogen, and star formation will slow down until the supply is depleted. Stars like our Sun can only last for 10 billion years or so; but the smallest, coolest red dwarfs can last for a few trillion years. However, thanks to the presence of dwarf galaxies and our impending merger with Andromeda, our galaxy could exist even longer.

However, all galaxies in this vicinity of the Universe will eventually become gravitationally bound to each other and merge into a giant elliptical galaxy. Astronomers have seen examples of these sorts of “fossil galaxies”, a good of which is Messier 49 – a supermassive elliptical galaxy.

These galaxies have used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.

After our galaxy merges with Andromeda, and goes on to merge with all other nearby galaxies in the local group, we can expect that it too will undergo a similar fate. And so, galaxy evolution has been occurring over billions of years, and it will continue to happen for the foreseeable future.

We have written many articles about galaxies for Universe Today. Here’s What is the Milky Way?, How did the Milky Way Form?, What Happens When Galaxies Collide?, What Happens When Galaxies Die?, A New Spin on Galactic Evolution, and Supercomputer will Study Galaxy Evolution,

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Sources:

October 6, 2016October 6, 2016 by Matt Williams

Can you buy Land on the Moon?

Astronauts need spacesuits to survive the temperature of the Moon. Image credit: NASA

Have you ever heard that it’s possible to buy property on the Moon? Perhaps someone has told you that, thanks to certain loopholes in the legal code, it is possible to purchase your very own parcel of lunar land. And in truth, many celebrities have reportedly bought into this scheme, hoping to snatch up their share of land before private companies or nations do.

Despite the fact that there may be several companies willing to oblige you, the reality is that international treaties say that no nation owns the Moon. These treaties also establish that the Moon is there for the good of all humans, and so it’s impossible for any state to own any lunar land. But does that mean private ownership is impossible too? The short answer is yes.

The long answer is, it’s complicated. At present, there are multiple nations hoping to build outposts and settlements on the Moon in the coming decades. The ESA hopes to build a “international village” between 2020 and 2030 and NASA has plans for its own for a Moon base.

The ESA recently elaborated its plan to create a Moon base by the 2030s. Credit: Foster + Partners is part of a consortium set up by the European Space Agency to explore the possibilities of 3D printing to construct lunar habitations. Credit: ESA/Foster + Partners — *The ESA recently elaborated its plan to create a Moon base by the 2030s. Credit: ESA/Foster + Partners*

The Russian space agency (Roscosmos) is planning to build a lunar base by the 2020s, and the China National Space Agency (CNSA) is planning to build such a base in a similar timeframe, thanks to the success of its Chang’e program.

Because of this, a lot of attention has been focused lately on the existing legal framework for the Moon and other celestial bodies. Let’s take a look at the history of “space law”, shall we?

Outer Space Treaty:

On Jan. 27th, 1967, the United States, United Kingdom, and the Soviet Union sat down together to work out a treaty on the exploration and use of outer space. With the Soviets and Americans locked in the Space Race, there was fear on all sides that any power that managed to put resources into orbit, or get to the Moon first, might have an edge on the others – and use these resources for evil!

As such, all sides signed “The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies” – aka. “The Outer Space Treaty”. This treaty went into effect on Oct. 10th, 1967, and became the basis of international space law. As of September 2015, it has been signed by 104 countries (while another 24 have signed the treaty but have not competed the ratification process).

Sample collection on the surface of the Moon. Apollo 16 astronaut Charles M. Duke Jr. is shown collecting samples with the Lunar Roving Vehicle in the left background. Image: NASA — *Astronaut Charles M. Duke Jr. shown collecting samples on the lunar surface with the Lunar Roving Vehicle during the Apollo 16 mission. Credit: NASA*

The treaty is overseen the United Nations Office for Outer Space Affairs (UNOOSA). It’s a big document, with lots of articles, subsections, and legalese. But the most relevant clause is Article II of the treaty, where it states:

“Outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.”

“Loophole” in the Treaty:

Despite clearly saying that Outer Space is the property of all humanity, and can only be used for the good of all, the language is specific to national ownership. As a result, there is no legal consensus on whether or not the treaty’s prohibition are also valid as far as private appropriation is concerned.

However, Article II addresses only the issue of national ownership, and contains no specific language about the rights of private individuals or bodies in owning anything in outer space. Because of this, there are some who have argued that property rights should be recognized on the basis of jurisdiction rather than territorial sovereignty.

*About 20 minutes after the first step, Aldrin joined Armstrong on the surface and became the second human to set foot on the Moon. Credit: NASA*

Looking to Article VI though, it states that governments are responsible for the actions of any party therein. So it is clear that the spirit of the treaty is meant to apply to all entities, be they public or private. As it states:

“States Parties to the Treaty shall bear international responsibility for national activities in outer space, including the moon and other celestial bodies, whether such activities are carried on by governmental agencies or by non-governmental entities, and for assuring that national activities are carried out in conformity with the provisions set forth in the present Treaty. The activities of non-governmental entities in outer space, including the moon and other celestial bodies, shall require authorization and continuing supervision by the appropriate State Party to the Treaty.”

In other words, any person, organization or company operating in space is answerable to their respective government. But since no specific mention is made of private ownership, there are those who claim that this represents a “loophole” in the treaty which allows them to claim and sell land on the Moon at this time. Because of this ambiguity, there have been attempts to augment the Outer Space Treaty.

The Moon Treaty:

On Dec. 18th, 1979, members of the United Nations presented an agreement which was meant to be a follow-up to the Outer Space Treaty and close its supposed loopholes. Known as the “Agreement Governing the Activities of States on the Moon and Other Celestial Bodies” – aka. “The Moon Treaty” or “Moon Agreement” – this treaty intended to establish a legal framework for the use of the Moon and other celestial bodies.

On the Lunar Surface – Apollo 11 astronauts trained on Earth to take individual photographs in succession in order to create a series of frames that could be assembled into panoramic images. This frame from fellow astronaut Buzz Aldrin’s panorama of the Apollo 11 landing site is the only good picture of mission commander Neil Armstrong on the lunar surface. Credit: NASA — *Buzz Aldrin’s panorama of the Apollo 11 landing site is the only good picture of mission commander Neil Armstrong on the lunar surface. Credit: NASA*

Much like the Outer Space Treaty, the agreement established that the Moon should be used for the benefit of all humanity and not for the sake of any individual state. The treaty banned weapons testing, declared that any scientific research must be open and shared with the international community, and that nations and individuals and organizations could not claim anything.

In practice, the treaty failed because it has not been ratified by any state that engages in crewed space exploration or has domestic launch capability. This includes the United States, the larger members of the ESA, Russia, China, Japan and India. Though it expressly forbids both national and private ownership of land on the Moon, or the use thereof for non-scientific, non-universal purposes, the treaty effectively has no teeth.

Bottom line, there is nothing that expressly forbids companies from owning land on the Moon. However, with no way to claim that land, anyone attempting to sell land to prospective buyers is basically selling snake oil. Any documentation that claims you own land on the Moon is unenforceable, and no nation on the planet that has signed either the Outer Space Treaty or the Moon Treaty will recognize it.

Moon Map — *The annotated features on the lunar nearside. You’ll notice, not one of them says “Land for Sale!” Credit: Wikimedia Commons/ Peter Freiman(Cmglee). Background photograph by Gregory H. Revera.*

Then again, if you were able to fly up to the Moon and build a settlement there, it would be pretty difficult for anyone to stop you. But don’t expect that to the be the last word on the issue. With multiple space agencies looking to create “international villages” and companies hoping to create a tourist industry, you could expect some serious legal battles down the road!

But of course, this is all academic. With no atmosphere to speak of, temperatures reaching incredible highs and lows – ranging from 100 °C (212 °F) to -173 °C (-279.4 °F) – its low gravity (16.5 % that of Earth), and all that harsh Moon dust, nobody outside of trained astronauts (or the clinically insane) should want to spend a significant amount of time there!

We have written many interesting articles about the Moon here at Universe Today. Here’s Can you Really Name a Star?, Make a Deal for Land on the Moon, and our series on Building a Moon Base.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Sources:

October 5, 2016October 6, 2016 by Matt Williams

What Were the First Lunar Landings?

A picture of Earth taken by Apollo 11 astronauts. Credit: NASA

The moment that the Apollo-11 mission touched down on the Moon, followed by Neil Armstrong‘s famous words – “That’s one small step for [a] man, one giant leap for mankind” – is one of the most iconic moments in history. The culmination of years of hard work and sacrifice, it was an achievement that forever established humanity as a space-faring species.

And in the year’s that followed, several more spacecraft and astronauts landed on the Moon. But before, during and after these missions, a number of other “lunar landings” were accomplished as well. Aside from astronauts, a number of robotic missions were mounted which were milestones in themselves. So exactly what were the earliest lunar landings?

Robotic Missions:

The first missions to the Moon consisted of probes and landers, the purpose of which was to study the lunar surface and determine where crewed missions might land. This took place during the 1950s where both the Soviet Space program and NASA sent landers to the Moon as part of their Luna and Pioneer programs.

*The Soviet Luna 2 probe, the first man-made object to land on the Moon. Credit: NASA*

After several attempts on both sides, the Soviets managed to achieve a successful lunar landing on Sept. 14th, 1959 with their Luna-2 spacecraft. After flying directly to the Moon for 36 hours, the spacecraft achieved a hard landing (i.e. crashed) on the surface west of the Mare Serenitatis – near the craters Aristides, Archimedes, and Autolycus.

The primary objective of the probe was to help confirm the discovery of the solar wind, turned up by the Luna-1 mission. However, with this crash landing, it became the first man-made object to touch down on the Moon. Upon impact, it scattered a series of Soviet emblems and ribbons that had been assembled into spheres, and which broke apart upon hitting the surface.

The next craft to make a lunar landing was the Soviet Luna-3 probe, almost a month after Luna-2 did. However, unlike its predecessor, the Luna-3 probe was equipped with a camera and managed to send back the first images of the far side of the Moon.

The first US spacecraft to impact the Moon was the Ranger-7 probe, which crashed into the Moon on July 31st, 1964. This came after a string of failures with previous spacecraft in the Pioneer and Ranger line of robotic spacecraft. Prior to impact, it too transmitted back photographs of the Lunar surface.

*The Ranger 7 lander, which became the first US spacecraft to land on the Moon. Credit: NASA*

This was followed by the Ranger-8 lander, which impacted the surface of the Moon on Feb. 20th, 1965. The spacecraft took 7,000 high-resolution images of the Moon before crashing onto the surface, just 24 km from the Sea of Tranquility, which NASA had been surveying for the sake of their future Apollo missions. These images, which yielded details about the local terrain, helped to pave the way for crewed missions.

The first spacecraft to make a soft landing on the Moon was the Soviet Luna-9 mission, on February 3rd, 1966. This was accomplished through the use of an airbag system that allowed the probe to survive hitting the surface at a speed of 50 km/hour. It also became the first spacecraft to transmit photographic data back to Earth from the surface of another celestial body.

The first truly soft landing was made by the US with the Surveyor-1 spacecraft, which touched down on the surface of the Moon on June 2nd, 1966. After landing in the Ocean of Storms, the probe transmitted data back to Earth that would also prove useful for the eventual Apollo missions.

Several more Surveyor missions and one more Luna mission landed on the Moon before crewed mission began, as part of NASA’s Apollo program.

Launch of Apollo 11. On July 16, 1969, the huge, 363-feet tall Saturn V rocket launches on the Apollo 11 mission from Pad A, Launch Complex 39, Kennedy Space Center, at 9:32 a.m. EDT. Onboard the Apollo 11 spacecraft are astronauts Neil A. Armstrong, commander; Michael Collins, command module pilot; and Edwin E. Aldrin Jr., lunar module pilot. Apollo 11 was the United States' first lunar landing mission. While astronauts Armstrong and Aldrin descended in the Lunar Module "Eagle" to explore the Sea of Tranquility region of the moon, astronaut Collins remained with the Command and Service Modules "Columbia" in lunar orbit. Image credit: NASA — *Launch of Apollo 11 mission aboard a Saturn V rocket on July 16th, 1969. Credit: NASA*

Crewed Missions:

The first crewed landing on the Moon was none other than the historic Apollo-11 mission, which touched down on the lunar surface on July 20th, 1969. After achieving orbit around the Moon in their Command Module (aka. the Columbia module), Neil Armstrong and Buzz Aldrin rode the Lunar Excursion (Eagle) Module down to the surface of the Moon.

Once they had landed, Armstrong radioed to Mission Control and announced their arrival by saying: “Houston, Tranquility Base here. The Eagle has landed.” Once the crew had gone through their checklist and depressurized the cabin, the Eagles’ hatch was opened and Armstrong began walking down the ladder to the Lunar surface first.

When he reached the bottom of the ladder, Armstrong said: “I’m going to step off the LEM now” (referring to the Lunar Excursion Module). He then turned and set his left boot on the surface of the Moon at 2:56 UTC July 21st, 1969, and spoke the famous words “That’s one small step for [a] man, one giant leap for mankind.”

About 20 minutes after the first step, Aldrin joined Armstrong on the surface and became the second human to set foot on the Moon. The two then unveiled a plaque commemorating their flight, set up the Early Apollo Scientific Experiment Package, and planted the flag of the United States before blasting off in the Lunar Module.

Aldrin on the Moon. Astronaut Buzz Aldrin walks on the surface of the moon near the leg of the lunar module Eagle during the Apollo 11 mission. Mission commander Neil Armstrong took this photograph with a 70mm lunar surface camera. While astronauts Armstrong and Aldrin explored the Sea of Tranquility region of the moon, astronaut Michael Collins remained with the command and service modules in lunar orbit. Image Credit: NASA — *Buzz Aldrin on the Moon during the Apollo 11 mission, with the reflection of Neil Armstrong visible in his face plate. Credit: NASA*

Several more Apollo missions followed which expanded on the accomplishments of the Apollo-11 crew. The US and NASA would remain the only nation and space agency to successfully land astronauts on the Moon, an accomplishment that has not been matched to this day.

Today, multiple space agencies (and even private companies) are contemplating returning to the Moon. Between NASA, the European Space Agency (ESA), the Russian Space Agency (Roscosmos), and the Chinese National Space Administration (CNSA), there are several plans for crewed missions, and even the construction of permanent bases on the Moon.

We have written many great articles about the Moon here at Universe Today. Here’s Who Were the First Men on the Moon?, How Many People Have Walked on the Moon?, How Do We Know the Moon Landing Isn’t Fake?, Where Were You When Apollo 11 Landed on the Moon?, What Does The Apollo 11 Moon Landing Site Look Like Today?

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Sources:

October 5, 2016October 5, 2016 by Matt Williams

What are Cepheid Variables?

Hubble image of variable star RS Puppis (NASA, ESA, and the Hubble Heritage Team)

The Universe is a really, really big place. We’re talking… imperceptibly big! In fact, based on decades worth of observations, astronomers now believe that the observable Universe measures about 46 billion light years across. The key word there is observable, because when you take into account that which we cannot see, scientists think it’s actually more like 92 billion light years across.

The hardest part in all of this is making accurate measurements of the distances involved. But since the birth of modern astronomy, increasingly accurate methods have evolved. Aside from redshift and examining the light coming from distant stars and galaxies, astronomers also rely on a class of stars known as Cepheid Variables (CVs) to determine the distance of objects within and beyond our Galaxy.

Definition:

Variable stars are essentially stars that experience fluctuations in their brightness (aka. absolute luminosity). Cepheids Variables are special type of variable star in that they are hot and massive – five to twenty times as much mass as our Sun – and are known for their tendency to pulsate radially and vary in both diameter and temperature.

What’s more, these pulsations are directly related to their absolute luminosity, which occurs within well-defined and predictable time periods (ranging from 1 to 100 days). When plotted as a magnitude vs. period relationship, the shape of the Cephiad luminosity curve resembles that of a “shark fin” – do its sudden rise and peak, followed by a steadier decline.

The name is derived from Delta Cephei, a variable star in the Cepheus constellation that was the first CV to be identified. Analysis of this star’s spectrum suggests that CVs also undergo changes in terms of temperature (between 5500 – 66oo K) and diameter (~15%) during a pulsation period.

Use in Astronomy:

The relationship between the period of variability and the luminosity of CV stars makes them very useful in determining the distance of objects in our Universe. Once the period is measured, the luminosity can be determined, thus yielding accurate estimates of the star’s distance using distance modulus equation.

This equation states that: m – M = 5 log d – 5 – where m is the apparent magnitude of the object, M is the absolute magnitude of the object, and d is the distance to the object in parsecs. Cepheid variables can be seen and measured to a distance of about 20 million light years, compared to a maximum distance of about 65 light years for Earth-based parallax measurements and just over 326 light years for the ESA’s Hipparcos mission.

*Calibrated Period-luminosity Relationship for Cepheids. Credit: NASA*

Because they are bright, and can be clearly seen million of light years away, they can be easily distinguished from other bright stars in their vicinity. Combined with the relationship between their variability and luminosity, this makes them highly useful tools in deducing the size and scale of our Universe.

Classes:

Cepheid variables are divided into two subclasses – Classical Cepheids and Type II Cepheids – based on differences in their masses, ages, and evolutionary histories. Classical Cepheids are Population I (metal-rich) variable stars that are 4-20 times more massive than the Sun and up to 100,000 times more luminous. They undergo pulsations with very regular periods on the order of days to months.

These Cepheids are typically yellow bright giants and supergiants (spectral class F6 – K2) and they experience radius changes in the millions of kilometers during a pulsation cycle. Classical Cepheids are used to determine distances to galaxies within the Local Group and beyond, and are a means by which the Hubble Constant can be established (see below).

Type II Cepheids are Population II (metal-poor) variable stars which pulsate with periods of typically between 1 and 50 days. Type II Cepheids are also older stars (~10 billion years) that have around half the mass of our Sun.

Type II Cepheids are also subdivided based on their period into the BL Her, W Virginis, and RV Tauri subclasses (named after specific examples) – which have periods of 1-4 days, 10-20 days, and more than 20 days, respectively. Type II Cepheids are used to establish the distance to the Galactic Center, globular clusters, and neighboring galaxies.

There are also those that do not fit into either category, which are known as Anomalous Cepheids. These variables have periods of less than 2 days (similar to RR Lyrae) but have higher luminosities. They also have higher masses than Type II Cepheids, and have unknown ages.

A small proportion of Cepheid variables have also been observed which pulsate in two modes at the same time, hence the name Double-mode Cepheids. A very small number pulsate in three modes, or an unusual combination of modes.

History of Observation:

The first Cepheid variable to be discovered was Eta Aquilae, which was observed on September 10th, 1784, by English astronomer Edward Pigott. Delta Cephei, for which this class of star is named, was discovered a few months later by amateur English astronomer John Goodricke.

In 1908, during an investigation of variable stars in the Magellanic Clouds, American astronomer Henrietta Swan Leavitt discovered the relationship between the period and luminosity of Classical Cepheids. After recording the periods of 25 different variables stars, she published her findings in 1912.

In the following years, several more astronomers would conduct research on Cepheids. By 1925, Edwin Hubble was able to establish the distance between the Milky Way and the Andromeda Galaxy based on Cepheid variables within the latter. These findings were pivotal, in that they settled the Great Debate, where astronomers sought to established whether or not the Milky Way was unique, or one of many galaxies in the Universe.

By gauging the distance between the Milky Way and several other galaxies, and combining it with Vesto Slipher’s measurements of their redshift, Hubble and Milton L. Humason were able to formulate Hubble’s Law. In short, they were able to prove that the Universe is in a state of expansion, something that had been suggested years prior.

Further developments during the 20th century included dividing Cepheids into different classes, which helped resolve issues in determining astronomical distances. This was done largely by Walter Baade, who in the 1940s recognized the difference between Classical and Type II Cepheids based on their size, age and luminosities.

Limitations:

Despite their value in determining astronomical distances, there are some limitations with this method. Chief among them is the fact that with Type II Cepheids, the relationship between period and luminosity can be effected by their lower metallicity, photometric contamination, and the changing and unknown effect that gas and dust have on the light they emit (stellar extinction).

These unresolved issues have resulted in different values being cited for Hubble’s Constant – which range between 60 km/s per 1 million parsecs (Mpc) and 80 km/s/Mpc. Resolving this discrepancy is one of the largest problems in modern cosmology, since the true size and rate of expansion of the Universe are linked.

However, improvements in instrumentation and methodology are increasing the accuracy with which Cepheid Variables are observed. In time, it is hoped that observations of these curious and unique stars will yield truly accurate values, thus removing a key source of doubt about our understanding of the Universe.

We have written many interesting articles about Cepheid Variables here at Universe Today. Here’s Astronomers Find New Way to Measure Cosmic Distances, Astronomers Use Light Echo to Measure the Distance to a Star, and Astronomers Closing in on Dark Energy with Refined Hubble Constant.

Astronomy Cast has an interesting episode that explains the differences between Population I and II stars – Episode 75: Stellar Populations.

Sources:

October 4, 2016November 5, 2016 by Matt Williams

Was SpaceX’s Lost Falcon 9 The Victim Of Sabotage?

Rocket lifting from Space Launch Complex 40, located at Cape Canaveral Air Force Station in Florida. Credit: SpaceX

On Sept. 1st, 2016, aerospace giant SpaceX suffered a terrible setback when one of their Falcon 9 rockets inexplicably exploded during a fueling test. An investigation into the causes of the accident – which Musk described as being the “most difficult and complex failure” in the company’s history – was immediately mounted.

And while the focus of the investigation has been on potential mechanical failures – such as a possible breach In 2nd stage helium system – another line in inquiry also came to light recently. In this case, the focus was on the ongoing feud between SpaceX and its greatest competitor, United Launch Alliance (ULA), and whether or not that could have played a role.

Speculation about this possible connection began after three unnamed industry officials who were familiar with the accident shared details of an incident that happened a few weeks after the explosion. According to The Washington Post, these officials claimed that SpaceX had come across something suspicious during the course of their investigation.

On Sept. 1st, one of SpaceX's Falcon 9 rocket's exploded during a static firing test. The company is now facing a potential legal battle over the damage caused. Credit: SpaceX — *On Sept. 1st, one of SpaceX’s Falcon 9 rocket’s exploded during a static firing test. The company is now facing a potential legal battle over the damage caused. Credit: SpaceX*

After pouring over images and video from the explosion, SpaceX investigators noticed an odd shadow and then a white spot on the roof of building located close to their launch complex. The building is currently being leased by ULA to refurbish their Sensible Modular Autonomous Return Technology (SMART) rocket motors – a key component in the company’s new Vulcan rocket.

Located about one and half kilometers (1 mile) from SpaceX’s launch facilities, and has a clear line of sight on the launch pad. SpaceX dispatched an representative to check it out, who arrived at the building and requested access to the roof. A ULA representative denied them access and called Air Force investigators, who then inspected the roof themselves and determined that nothing of a suspicions nature was there.

While the incident proved to be inconclusive, it is the fact that it was not previously reported that is raising some eyebrows. And it is just another mysterious detail to come from an accident that remains largely unexplained. However, in all likelihood the incident was avoided to prevent embarrassment to either company, and to avoid fueling speculations about possible sabotage (which seems highly unlikely at this point).

In the meantime, SpaceX is still investigating the explosion with the help of NASA, the Federal Aviation Administration (FAA), the USAF’s 45th Space Wing. Musk commented on the ongoing investigation while attending the International Astronautical Congress in Guadalajara, Mexico.

*Mangled SpaceX Falcon 9 strongback after prelaunch explosion destroyed the rocket and AMOS-6 payload and damaged the pad. Credit: Ken Kremer/kenkremer.com*

In the midst of sharing the latest details of his vision to colonize Mars, Musk was quoted by The Washington Post as saying that the investigation is his company’s “absolute top priority.” As for the cause, he went on to say that they have “eliminated all of the obvious possibilities for what occurred there. So what remains are the less probable answers.”

Whether or not sabotage is a realistic possibility, this incident does serve to highlight the rivalry between SpaceX and ULA. Prior to 2014, ULA was the sole provider of launch services for the US Air Force, until a lawsuit from SpaceX compelled them to open the field to competition. Since then, both companies have been fighting – sometimes bitterly – to secure national security contracts.

It has also brought the issue of government oversight and accountability to the fore. On Sept. 29th, members of Congress Mike Coffman (R-Co) and Robert Aderholt (R-Al) sent a congressional letter to the heads of NASA, the US Air Force and the FAA expressing concerns about SpaceX’s recent accidents and the need for “assured access to space”.

In the letter, Coffman and Aderholt indicated that authority for investigating this and other accidents involving commercial space companies should be entrusted to the federal government:

“The investigative responses to both SpaceX failures raise serious concerns about the authority provided to commercial providers and the protection of national space assets. In both Falcon 9 explosions, NASA and the FAA granted primary responsibility for conducting the mishap investigation to SpaceX. Although subject to FAA oversight, it can be asserted the investigation lacked the openness taxpayers would expect before a return-to-flight.”

*SpaceX Falcon 9 rocket explodes about 2 minutes after liftoff from Cape Canaveral Air Force Station in Florida on June 28, 2015. Credit: Ken Kremer/kenkremer.com*

In other words, several Republican members of Congress hope to make SpaceX’s return to flight contingent on more stringent federal oversight. This may prove to be a source of inconvenience for SpaceX, which has stated that they intend to return to regular flights with their Falcon 9 rockets by November 1st.

Then again, increased federal oversight may also be beneficial in the long run. As is stated in the letter, both accidents involving SpaceX in the past few months occurred after the USAF signed off on the rockets involved:

“Both accidents occurred after the Air Force certified the Falcon 9 launch vehicle for U.S. national security launches, less than fifteen months ago. The certification, designed to subject the Falcon 9’s design and manufacturing process to a review of their technical and manufacturing rigor, appears to have fallen short of ensuring reliable assured US access to space for our most important payloads.”

Clearly, something is wrong if technical failures are not being caught in advance. But then again, space exploration is a hard business, and even the most routine checks can’t account for everything. Nevertheless, if there’s one thing that the Space Race taught us, it is that fierce competition can lead to mistakes, which can in turn cost lives.

As such, demanding that the federal authorities be on hand to ensure that safety standards are met, and that all competitors are being subjected to the same regulatory framework (without preference), might not be a bad idea.

Further Reading: The Washington Post