Space and astronomy news
Host: Fraser Cain (@fcain)
Guests:
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Ramin Skibba (@raminskibba)
Dave Dickinson (@astroguyz / www.astroguyz.com)
Continue reading “Weekly Space Hangout – Jan. 23, 2015: SpaceX, Rosetta, and Asteroid Updates!”
The current most-used Solar System mnemonic for remembering the planets and their order from the Sun is “My Very Educated Mother Just Served Us Noodles.” But, it’s the “Year of the Dwarf Planet” and some folks are hoping all the dwarfs of our Solar System will get a little more respect and possibly be considered “real” planets.
A group of science writers from The New York Times are among those who are “rooting for the dwarf planets to be considered actual planets.” But if that were to happen, one issue would be that we’d need a new memorization mnemonic (I know… this is a a horrible dilemma.)
It wouldn’t be just adding P for Pluto (and reverting back to the old “My Very Excellent Mother Just Served Us Nine Pizzas) — you’d have to add a C in the middle for Ceres, along with E for Eris, H for Haumea and M for Makemake at the end.
So, Universe Today readers, let’s help The New York Times find some new mnemonics.
Here would be the order:
Mercury
Venus
Earth
Mars
Ceres
Jupiter
Saturn
Uranus
Neptune
Pluto
Haumea
Makemake
Eris
And while we’re at it, we’ll take suggestions for a new (family friendly, please) mnemonic for the current 8 planets we have, something without Mothers and Noodles, perhaps. Planet hunter Mike Brown from Caltech (one of the folks responsible for all this planet arguing) has suggested “Mean Very Evil Men Just Shortened Up Nature.”
Put your ideas in the comments below.
It’s always good to get a little change of perspective, and with this image we achieve just that: it’s a view of Mercury’s north pole projected as it might be seen from above a slightly more southerly latitude. Thanks to the MESSENGER spacecraft, with which this image was originally acquired, as well as the Arecibo Observatory here on Earth, scientists now know that these polar craters contain large deposits of water ice – which may seem surprising on an airless and searing-hot planet located so close to the Sun but not when you realize that the interiors of these craters never actually receive sunlight.
The locations of ice deposits are shown in the image in yellow. See below for a full-sized version.
The five largest ice-filled craters in this view are (from front to back) the 112-km-wide Prokofiev and the smaller Kandinsky, Tolkien, Tryggvadottir, and Chesterton craters. A mosaic of many images acquired by MESSENGER’s Mercury Dual Imaging Sustem (MDIS) instrument during its time in orbit, you would never actually see a view of the planet’s pole illuminated like this in real life but orienting it this way helps put things into…well, perspective.
Radar-bright regions in Mercury’s polar craters have been known about since 1992 when they were first imaged from the Arecibo Observatory in Puerto Rico. Located in areas of permanent shadow where sunlight never reaches (due to the fact that Mercury’s axial tilt is a mere 2.11º, unlike Earth’s much more pronounced 23.4º slant) they have since been confirmed by MESSENGER observations to contain frozen water and other volatile materials.
Read more: Ice Alert! Mercury’s Deposits Could Tell Us More About How Water Came To Earth
Similarly-shadowed craters on our Moon’s south pole have also been found to contain water ice, although those deposits appear different in composition, texture, and age. It’s suspected that some of Mercury’s frozen materials may have been delivered later than those found on the Moon, or are being restored via an ongoing process. Read more about these findings here.
Explore Mercury’s shadowed craters with the Water Ice Data Exploration (WIDE) app
In orbit around Mercury since 2011, MESSENGER is now nearing the end of its operational life. Engineers have figured out a way to extend its fuel use for an additional month, possibly delaying its inevitable descent until April, but even if this maneuver goes as planned the spacecraft will be meeting Mercury’s surface very soon.
Source: MESSENGER
Where on Earth did our water come from. Well, obviously not from Earth, of course, but from space. But did it come from comets, or did the water form naturally right here in the Solar System, and the Earth just scooped it up?
Continue reading “Astronomy Cast Ep. 363: Where Did The Earth’s Water Come From?”
Venus is often referred to as our “sister planet,” due to the many geophysical similarities that exist between it Earth. For starters, our two planets are close in mass, with Venus weighing in at 4.868 x 1024 kg compared to Earth’s 5.9736×1024 kg. In terms of size, the planets are almost identical, with Venus measuring 12,100 km in diameter and Earth 12,742 km.
In terms of density and gravity, the two are neck and neck – with Venus boasting 86.6% of the former and 90.7% of the latter. Venus also has a thick atmosphere, much like our own, and it is believed that both planets share a common origin, forming at the same time out of a condensing clouds of dust particles around 4.5 billion years ago.
However, for all the characteristics these two planets have in common, average temperature is not one of them. Whereas the Earth has an average surface temperature of 14 degrees Celsius, the average temperature of Venus is 460 degrees Celsius. That is roughly 410 degrees hotter than the hottest deserts on our planet.
In fact, at a searing 750 K (477 °C), the surface of Venus is the hottest in the solar system. Venus is closer to the Sun by 108 million km, (about 30% closer than the Earth), but it is mainly due to the planet’s thick atmosphere. Unlike Earth’s, which is composed primarily of nitrogen, oxygen and ozone, Venus’ atmosphere is an incredibly dense cloud of carbon dioxide and sulfur dioxide gas.
The combination of these gases in high concentrations causes a catastrophic greenhouse effect that traps incident sunlight and prevents it from radiating into space. This results in an estimated surface temperature boost of 475 K (201.85 °C), leaving the surface a molten, charred mess that nothing (that we know of) can live on. Atmospheric pressure also plays a role, being 91 times that of what it is here on Earth; and clouds of toxic vapor constantly rain sulfuric acid on the surface.
In addition, the surface temperature on Venus does not vary like it does here on Earth. On our planet, temperatures vary wildly due to the time of year and even more so based on the location on our planet. The hottest temperature ever recorded on Earth was 70.7°C in the Lut Desert of Iran in 2005. On the other end of the spectrum, the coldest temperature ever recorded on Earth was in Vostok, Antarctica at -89.2 C.
But on Venus, the surface temperature is 460 degrees Celsius, day or night, at the poles or at the equator. Beyond its thick atmosphere, Venus’ axial tilt (aka. obliquity) plays a role in this temperature consistency. Earth’s axis is tilted 23.4 ° in relation to the Sun, whereas Venus’ is only tilted by 3 °.
The only respite from the heat on Venus is to be found around 50 km into the atmosphere. It is at that point that temperatures and atmospheric pressure are equal to that of Earth’s. It is for this reason that some scientists believe that floating habitats could be constructed here, using Venus’ thick clouds to buoy the habitats high above the surface. Additionally, in 2014, a group of mission planners from NASA Langely came up with a mission to Venus’ atmosphere using airships.
These habitats could play an important role in the terraforming of Venus as well, acting as scientific research stations that could either fire off the excess atmosphere off into space, or introduce bacteria or chemicals that could convert all the CO2 and SO2 into a hospitable, breathable atmosphere.
Beyond the fact that it is a hot and hellish landscape, very little is known about Venus’ surface environment. This is due to the thick atmosphere, which has made visual observation impossible. The sulfuric acid is also problematic since clouds composed of it are highly reflective of visible light, which prevents optical observation. Probes have been sent to the surface in the past, but the volatile and corrosive environment means that anything that lands there can only survive for a few hours.
What little we know about the planet’s surface has come from years worth of radar imaging, the most recent of which was conducted by NASA’s Magellan spacecraft (aka. the Venus Radar Mapper). Using synthetic aperture radar, the robotic space probe spent four years (1990-1994) mapping the surface of Venus and measuring its gravitational field before its orbit decayed and it was “disposed of” in the planet’s atmosphere.
The images provided by this and other missions revealed a surface dominated by volcanoes. There are at least 1,000 volcanoes or volcanic centers larger than 20 km in diameter on Venus’ harsh landscape. Many scientists believe Venus was resurfaced by volcanic activity 300 to 500 million years ago. Lava flows are a testament to this, which appear to have produced channels of hardened magma that extend for hundreds of km in all directions. The mixture of volcanic ash and the sulfuric acid clouds is also known to produce intense lightning and thunder storms.
The temperature of Venus is not the only extreme on the planet. The atmosphere is constantly churned by hurricane force winds reaching 360 kph. Add to that the crushing air pressure and rainstorms of sulfuric acid, and it becomes easy to see why Venus is such a barren, lifeless rock that has been hard to explore.
We have written many articles about Venus for Universe Today. Here are some interesting facts about Venus, and here’s an article about Venus Greenhouse Effect. And here is an article about the many interesting pictures taken of Venus over the past few decades.
If you’d like more information on Venus, check out Hubblesite’s News Releases about Venus, and here’s a link to NASA’s Solar System Exploration Guide on Venus.
We’ve also recorded an entire episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus.
Reference:
NASA
Maria Zuber is one of the hardest working scientists in planetary science, being a part of six different space missions to explore the Solar System. Currently, she’s the lead investigator for NASA’s GRAIL mission.
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Our Solar System is an immense and amazing place. Between its eight planets, 176 moons, 5 dwarf planets (possibly hundreds more), 659,212 known asteroids, and 3,296 known comets, it has wonders to sate the most demanding of curiosities. Our Solar System is made up of different regions, which are delineated based on their distance from the Sun, but also the types of planets and bodies that can be found within them.
In the inner Solar System, we find the “Inner Planets” – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.
For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterparts. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.
This region is also within the “frost line,” which is a little less than 5 AU (about 700 million km) from the Sun. This line represents the boundary in a system where conditions are warm enough that hydrogen compounds such as water, ammonia, and methane are able to take liquid form. Beyond the frost line, these compounds condense into ice grains.Some scientists refer to the frost line as the “Goldilocks Zone” — where conditions for life may be “just right.”
Generally, inner planets are smaller and denser than their counterparts, and have few to no moons or rings circling them. The outer planets, meanwhile, often have dozens of satellites and rings composed of particles of ice and rock.
The terrestrial inner planets are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather. All of them have impact craters and tectonic surface features as well, such as rift valleys and volcanoes.
Of the inner planets, Mercury is the closest to our Sun and the smallest of the terrestrial planets. This small planet looks very much like the Earth’s Moon and is even a similar grayish color, and it even has many deep craters and is covered by a thin layer of tiny particle silicates.
Its magnetic field is only about 1 percent that of Earth’s, and it’s very thin atmosphere means that it is hot during the day (up to 430°C) and freezing at night (as low as -187 °C) because the atmosphere can neither keep heat in or out. It has no moons of its own and is comprised mostly of iron and nickel. Mercury is one of the densest planets in the Solar System.
Venus, which is about the same size as Earth, has a thick toxic atmosphere that traps heat, making it the hottest planet in the Solar System. This atmosphere is composed of 96% carbon dioxide, along with nitrogen and a few other gases. Dense clouds within Venus’ atmosphere are composed of sulphuric acid and other corrosive compounds, with very litter water.
Only two spacecraft have ever penetrated Venus’s thick atmosphere, but it’s not just man-made objects that have trouble getting through. There are fewer crater impacts on Venus than other planets because all but the largest meteors don’t make it through the thick air without disintegrating. Much of Venus’ surface is marked with volcanoes and deep canyons — the biggest of which is over 6400 km (4,000 mi) long.
Venus is often called the “morning star” because, with the exception of Earth’s moon, it’s the brightest object we see in the sky. Like Mercury, Venus has no moon of its own.
Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that currently has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight and warmth in, which is also essential for life to survive.
Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our Moon, the only one we have, is comprised of a mixture of various rocks and minerals.
Mars is the fourth and final inner planet, and also known as the “Red Planet” due to the rust of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mountain in the Solar System – Olympus Mons – which rises some 21,229 m (69,649 ft) above the surface, and a giant canyon called Valles Marineris. Valles Marineris is 4000 km (2500 mi) long and reaches depths of up to 7 km (4 mi)!
For comparison, the Grand Canyon in Arizona is about 800 km (500 mi) long and 1.6 km (1 mi) deep. In fact, the extent of Valles Marineris is as long as the United States and it spans about 20 percent (1/5) of the entire distance around Mars. Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well.
At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one.
Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, but has since evaporated into space. The planet has two small moons called Phobos and Deimos.
Beyond Mars are the four outer planets: Jupiter, Saturn, Uranus, and Neptune.
We have written many interesting articles about the inner planets here at Universe Today. Here’s The Solar System Guide as well as The Inner and Outer Planets in Our Solar System.
For more information, check out this article from NASA on the planets of the Solar System and this article from Solstation about the inner planets.
Astronomy Cast also has episodes on all of the inner planets including this one about Mercury.
The Earth is often compared to a majestic blue marble, especially by those privileged few who have gazed upon it from orbit. This is due to the prevalence of water on the planet’s surface. While water itself is not blue, water gives off blue light upon reflection.
For those of us confined to living on the surface, the fact that our world is mostly covered in water is a well known fact. But how much of our planet is made up of water, exactly? Like most facts pertaining to our world, the answer is a little more complicated than you might think, and takes into account a number of different qualifications.
In simplest terms, water makes up about 71% of the Earth’s surface, while the other 29% consists of continents and islands. To break the numbers down, 96.5% of all the Earth’s water is contained within the oceans as salt water, while the remaining 3.5% is freshwater lakes and frozen water locked up in glaciers and the polar ice caps.
Of that fresh water, almost all of it takes the form of ice: 69% of it, to be exact. If you could melt all that ice, and the Earth’s surface was perfectly smooth, the sea levels would rise to an altitude of 2.7 km.
Aside from the water that exists in ice form, there is also the staggering amount of water that exists beneath the Earth’s surface. If you were to gather all the Earth’s fresh water together as a single mass (as shown in the image above) it is estimated that it would measure some 1,386 million cubic kilometers (km3) in volume.
Meanwhile, the amount of water that exists as groundwater, rivers, lakes, and streams would constitute just over 10.6 million km3, which works out to a little over 0.7%. Seen in this context, the limited and precious nature of freshwater becomes truly clear.
But how much of Earth is water – i.e. how much water contributes to the actual mass of the planet? This includes not just the surface of the Earth, but inside as well. In terms of volume, all of the water on Earth works out to about 1.386 billion cubic kilometers (km³) or 332.5 million cubic miles (mi³) of space.
But in terms of mas, scientists calculate that the oceans on Earth weight about 1.35 x 1018 metric tonnes (1.488 x 1018 US tons), which is the equivalent of 1.35 billion trillion kg, or 2976 trillion trillion pounds. This is just 1/4400 the total mass of the Earth, which means that while the oceans cover 71% of the Earth’s surface, they only account for 0.02% of our planet’s total mass.
The origin of water on the Earth’s surface, as well as the fact that it has more water than any other rocky planet in the Solar System, are two of long-standing mysteries concerning our planet. Not that long ago, it was believed that our planet formed dry some 4.6 billion years ago, with high-energy impacts creating a molten surface on the infant Earth.
According to this theory, water was brought to the world’s oceans thanks to icy comets, trans-Neptunian objects or water-rich meteoroids (protoplanets) from the outer reaches of the main asteroid belt colliding with the Earth.
However, more recent research conducted by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts, has pushed the date of these origins back further. According to this new study, the world’s oceans also date back 4.6 billion years, when all the worlds of the inner Solar System were still forming.
This conclusion was reached by examining meteorites thought to have formed at different times in the history of the Solar System. Carbonaceous chondrite, the oldest meteorites that have been dated to the very earliest days of the Solar System, were found to have the same chemistry as those originating from protoplanets like Vesta. This includes a significance presence of water.
These meteorites are dated to the same epoch in which water was believed to have formed on Earth – some 11 million years after the formation of the Solar System. In short, it now appears that meteorites were depositing water on Earth in its earliest days.
While not ruling out the possibility that some of the water that covers 71 percent of Earth today may have arrived later, these findings suggest that there was enough already here for life to have begun earlier than thought.
We’ve written many articles about the oceans for Universe Today. Here’s How Many Oceans are there in the World?, Earth Has Less Water Than You Think, Where Did Earth’s Water Come From?, Why Doesn’t Earth Have More Water?, Rethinking the Source of Earth’s Water.
If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth and Episode 363: Where Did Earth’s Water Come From?
Sources:
One day – and it really is only matter of time – humans will set foot on the surfaces of other far-flung worlds in our Solar System, leaving the Earth and Moon far behind to wander the valleys of Mars, trek across the ice of Europa, and perhaps even soar through the skies of Titan like winged creatures from ancient legends. But until then we must rely on the exploration of our robotic emissaries and our own boundless imagination and curiosity to picture what such voyages would be like. Here in “Wanderers,” video artist Erik Wernquist has used both resources in abundance to visualize fascinating off-world adventures yet to be undertaken by generations to come.
Continue reading “This Short Film is a Stunning Preview of Human Space Exploration”
If you’ve ever stood outside after twilight has passed, or a few hours before the sun rises at dawn, then chances are you’ve witnessed the phenomenon known as zodiacal light. This effect, which looks like a faint, diffuse white glow in the night sky, is what happens when sunlight is reflected off of tiny particles and appears to extend up from the vicinity of the Sun. This reflected light is not just observed from Earth but can be observed from everywhere in the Solar System.
Using the full power of the Very Large Telescopic Interferometer (VLTI), an international team of astronomers recently discovered that the exozodiacal light – i.e., zodiacal light around other star systems – close to the habitable zones around nine nearby stars was far more extreme. The presence of such large amounts of dust in the inner regions around some stars may pose an obstacle to the direct imaging of Earth-like planets.
The reason for this is simple: even at low levels, exozodiacal dust causes light to become amplified intensely. For example, the light detected in this survey was roughly 1000 times brighter than the zodiacal light seen around the Sun. While this exozodiacal light had been previously detected, this is the first large systematic study of this phenomenon around nearby stars.
The team used the VLTI visitor instrument PIONIER which is able to interferometrically connect all four Auxiliary Telescopes or all four Unit Telescopes of the VLTI at the Paranal Observatory. This led to not only extremely high resolution of the targets but also allowed for a high observing efficiency.
In total, the team observed exozodiacal light from hot dust close to the habitable zones of 92 nearby stars and combined the new data with their earlier observations.
In contrast to these earlier observations – which were made with the Center for High Angular Resolution Astronomy (CHARA) array at Georgia State University – the team did not observe dust that will later form into planets, but dust created in collisions between small planets of a few kilometers in size – objects called planetesimals that are similar to the asteroids and comets of the Solar System. Dust of this kind is also the origin of the zodiacal light in the Solar System.
As a by-product, these observations have also led to the discovery of new, unexpected stellar companions orbiting around some of the most massive stars in the sample. “These new companions suggest that we should revise our current understanding of how many of this type of star are actually double,” says Lindsay Marion, lead author of an additional paper dedicated to this complementary work using the same data.
“If we want to study the evolution of Earth-like planets close to the habitable zone, we need to observe the zodiacal dust in this region around other stars,” said Steve Ertel, lead author of the paper, from ESO and the University of Grenoble in France. “Detecting and characterizing this kind of dust around other stars is a way to study the architecture and evolution of planetary systems.”
However, the good news is that the number of stars containing zodiacal light at the level of our Solar System is most likely much higher than the numbers found in the survey.
“The high detection rate found at this bright level suggests that there must be a significant number of systems containing fainter dust, undetectable in our survey, but still much brighter than the Solar System’s zodiacal dust,” explains Olivier Absil, co-author of the paper, from the University of Liège. “The presence of such dust in so many systems could therefore become an obstacle for future observations, which aim to make direct images of Earth-like exoplanets.”
Therefore, these observations are only a first step towards more detailed studies of exozodiacal light, and need not dampen our spirits about discovering more Earth-like exoplanets in the near future.
Further Reading: ESO