Matt Williams is a space journalist and science communicator for Universe Today and Interesting Engineering. He's also a science fiction author, podcaster (Stories from Space), and Taekwon-Do instructor who lives on Vancouver Island with his wife and family.
A planetary mass object the size of Mars would be sufficient to produce the observed perturbations in the distant Kuiper Belt. (Image: Heather Roper/LPL)
Astronomers have known about the Kuiper Belt for decades, and were postulating about its existence long before it was even observed. Since that time, many discoveries have been made in this region of space – ranging from numerous minor planets to the fact that the orbital planes of Kuiper Belt Objects (KBOs) are widely dispersed – that have led to new theoretical models of the formation and evolution of the Solar System.
For instance, while conducting measurements of the mean plane of minor planets and KBOs, a team from the Lunar and Planetary Laboratory (LPL) at The University of Arizona discovered a warp in orbits of certain, highly-distant KBOs. According to their study, this warp could be an indication of a planetary-mass object in the area, one which orbits our Sun even closer than the theoretical “Planet 9“.
The study – “The Curiously Warped Mean Plane of the Kuiper Belt” which is scheduled to be published in the Astronomical Journal – was produced by Kathryn Volk and Renu Malhotra (two astronomers with the LPL). As they stated in their study, the presence of this planet was confirmed by examining the orbits of icy bodies in the very outer reaches of the Solar System.
Artist’s impression of the yet-to-be-discovered “planetary mass object”, who’s existence has been theorized based on the orbital plane of distant Kuiper Belt objects. Credit: Heather Roper/LPL
Whereas most KBOs – which are leftover material from the formation of the Solar System – orbit the Sun close to the mean plane of the Solar System itself, the most distant objects do not. To determine why, the researchers analyzed the tilt angles of the orbital planes of more than 600 KBOs to determine the direction of their precession – i.e. the direction in which these rotating objects experience a change in their orientation.
As Malhotra – a Louise Foucar Marshall Science Research Professor and Regents’ Professor of Planetary Sciences at LPL – illustrated, KBOs operate in a way that is analogous to spinning tops:
“Imagine you have lots and lots of fast-spinning tops, and you give each one a slight nudge. If you then take a snapshot of them, you will find that their spin axes will be at different orientations, but on average, they will be pointing to the local gravitational field of Earth… We expect each of the KBOs’ orbital tilt angle to be at a different orientation, but on average, they will be pointing perpendicular to the plane determined by the Sun and the big planets.”
What they found was that the average plane of these objects was tilted away from the solar plane by about eight degrees, which suggests that a powerful gravitational force in the outer Solar System is tugging on them. “The most likely explanation for our results is that there is some unseen mass,” said Volk in UA News press release. “According to our calculations, something as massive as Mars would be needed to cause the warp that we measured.”
Animated diagram showing the spacing of the Solar Systems planet’s, the unusually closely spaced orbits of six of the most distant KBOs, and the possible “Planet 9”. Credit: Caltech/nagualdesign
According to their calculations, this Mars-size body would likely orbit the Sun at a distance of roughly 60 AU, and with an orbital inclination that was tilted eight degrees to the average plane of the known planets (i.e. the same tilt as the “warped” KBOs). Within these parameters, a planet of this size would have sufficient gravitational influence to warp the orbital plane of the distant KBOs to within 10 AU on either side of it.
In other words, a Mars-sized planet in the outer Kuiper Belt would be able to influence the orbital inclination of KBOs that are between 50 and 70 AUs from the Sun. This is certainly consistent with what we know about the Kuiper Belt, who’s orbital inclination appears to be consistently flat (i.e. consistent with the rest of the Solar System) past a distance of about 50 AU – but changes between a distance of 50 and 80 AU.
As Volk indicated, there is a possibility that this warping could be the result of a statistical fluke. But in the end, their calculations indicated that this is highly unlikely, and that the behavior of distant KBOs is consistent with the existence of a as-yet-unseen gravitational influence:
“But going further out from 50 to 80 AU, we found that the average plane actually warps away from the invariable plane. There is a range of uncertainties for the measured warp, but there is not more than 1 or 2 percent chance that this warp is merely a statistical fluke of the limited observational sample of KBOs… The observed distant KBOs are concentrated in a ring about 30 AU wide and would feel the gravity of such a planetary mass object over time, so hypothesizing one planetary mass to cause the observed warp is not unreasonable across that distance.”
Artist’s impression of Planet Nine, blocking out the Milky Way. The Sun is in the distance, with the orbit of Neptune shown as a ring. Credit: ESO/Tomruen/nagualdesign
Another possibility is that another object entirely could have disturbed the plane of the outer Kuiper Belt – for instance, a star passing through the outer Solar System. But as Malhotra explained, this explanation is also a highly unlikely, as any disturbance caused by a passing star would only be temporary and would have manifested itself differently.
“A passing star would draw all the ‘spinning tops’ in one direction,” he said. “Once the star is gone, all the KBOs will go back to precessing around their previous plane. That would have required an extremely close passage at about 100 AU, and the warp would be erased within 10 million years, so we don’t consider this a likely scenario.”
Moreover, the tilt of these objects could not be attributed to the existence of Planet 9, who’s existence has also been suggested based on the extreme eccentricity of certain populations of KBOs. Compared to this Mars-sized planet that is thought to orbit at 60 AUs from the Sun, Planet 9 is predicted to be much more massive (at around 10 Earth masses) and is believed to orbit at a distance of 500 to 700 AU.
Naturally, one has to ask why this planetary-mass body has not been found yet. According to Volk and Malhotra, the reason has to do with the fact that astronomers have not yet searched the entire sky for distant for Solar System objects. Beyond that, there’s also the likely position of the object (within the galactic plane), which is so densely packed with stars that surveys would have a hard time spotting it.
However, with the construction of instruments like the Large Synoptic Survey Telescope (LSST) in Chile nearly complete, opportunities to spot it may be coming sooner other than later. This wide-field survey reflecting telescope, which is run by a consortium that includes the University of Arizona, is expected to provide some of the deepest and widest views of the Universe to date (which will begin in 2020).
In the meantime, and in response to any possible controversies regarding the so-called “Planet Debate”, it is worth noting that this body (if it exists) is currently being referred to as “planetary-mass object”. This is because, by definition, a body needs to have cleared its orbit in order to be called a planet. What’s more, the study does not rule out the possibility that the warp could be the result of more than one planetary mass object in the area.
Therefore, it would premature to state that astronomers – having not yet even confirmed the existence of Planet 9 – are now talking about the existence of a possible “Planet 10”. In the coming years, more news and information will become available, which will hopefully help us put the debate to rest and agree on just how many planets there are out there!
The picture shows an imaginary snake robot on Space Station – on the way to inspect anything for the astronaut. Credit: SINTEF
Human space exploration is going to kick into high gear in the coming decades. Within the inner Solar System alone, missions are being planned that will see robotic explorers and crews sent to Near Earth Objects (NEOs), back to the Moon, and even on to Mars. Beyond that, there are even plans to send robotic missions to Europa, Enceladus, Titan, and other “ocean worlds” to look for signs of life.
In all cases, questions natural arise as to what kinds of missions will be most suited to them. In the case of places like Titan (which have low gravity and dense atmospheres) aerial drones are considered the best bet. But when it comes to rocky place like asteroids, the Moon and Mars, the best candidate may be robot snakes, which could find their way through tight spaces and travel underground.
This concept was proposed three years ago by the Foundation for Scientific and Industrial Research (SINTEF), the largest independent research organization in Scandinavia. As part of a project commissioned by the ESA – known as SERPEX – they began studying how robots designed to mimic the movements of snakes could assist astronauts aboard the International Space Station.
SINTEF researchers Pål Liljebäck and Aksel Transeth, and Knut Robert Fossum of NTNU’s CIRiS, playing with Wheeko the snake robot. Credit: SINTEF/Thor Nielsen.
But as Aksel Transeth, a senior research scientist at SINTEF, explained in a recent press statement, the possibilities go far beyond the ISS:
“More ambitious applications include potential activities on comets and the Moon. [A] Snake Robot that can assist ISS astronauts in maintaining their equipment is perhaps a solution which can be possible to realize on a more short term.”
Compared to other robotic explorers, the main selling point of a robot snake is that it offers better mobility. For two decades now, NASA has been exploring the Red Planet with robotic rovers, starting with Pathfinder and Sojourner in 1997, Spirit and Opportunity in 2003, and then Curiosity in 2012. And in a little over two years, they will be sending the Mars 2020 rover.
In all cases, these robots get around on six wheels and conduct experiments using instruments on robotic arms. But as the missions teams behind these rovers have learned, mobility can be a challenge. For instance, after five years on the Martian surface, the Spirit rover became stuck in soft soil, where its mission ended. And as successful as these missions have been at conducting research, there are locations that they simply can’t get to.
The SINTEF researchers decided to tackle these issues through biomimicry – i.e. robots that mimic the functions of living creatures. By combining a rover that can navigate over large distances with a snake robot that can crawl along the ground and get into inaccessible places, they believe that future missions would be able to go places and collect samples in ways that other missions could not.
The ESA recently elaborated its plan to create a Moon base by the 2030s. Credit: ESA/Foster+Partners
As Transeth explained back in 2013, this pairing would open up all kinds of possibilities. “We are looking at several alternatives to enable a rover and a robot to work together,” he said. “Since the rover has a powerful energy source, it can provide the snake robot with power through a cable extending between the rover and the robot. If the robot had to use its own batteries, it would run out of power and we would lose it.”
In the configuration Transeth and his colleagues are envisioning, the rover would handle the task of traveling over long distances and then be able to dispatch the snake to crawl into tight inaccessible areas. They would be connected by a cable that would provide electricity, communication signals and would be used to pull the snake back in. In this sense, the snake would act like one of the rover’s arms, but would have the ability to travel autonomously.
“We believe that we can design a robot that can hold on, roll itself up and then extend its body in order to reach new contact points,” said Transeth. “Moreover, we believe that it can creep in among equipment components on the ISS and use equipment surfaces to gain traction in order to keep moving forward – much in the same way as real snakes do in the wild.”
On Mars, sample collection is crucial to many space agency’s research. For the Curiosity rover, the presence of hydrated minerals and clays in soil samples confirmed that Mars once had a warmer, wetter climate. And in the future, scientists hope to find biomakers in Martian soil that could indicate the presence (past or present) of biological life. In this respect, a snake robot would prove very useful since it could access underground recesses the rover cannot.
The sinuous rille known as Rima Ariadaeus, as photographed from Apollo 10, which is the result of a collapsed lava tube. Credit: NASA
On the Moon, snake robots could be especially useful in helping the ESA establish it’s proposed “Moon Village” – a permanent base for scientific activity, tourism and mining that would also act as a successor to the ISS. The most likely location for this base could be within stable lava tubes or subterranean tunnels, which would provide natural shielding from meteors, solar radiation and cosmic rays.
But before such construction of this base can take place, these tunnels and lava tubes will have to be inspected to ensure that they are safe for human habitation. The ESA has also been committed to studying comets in recent years, which included sending the Rosetta space probe and Philae lander to rendezvous with the comet 67P/Tsjurjumov–Gerasimenko in 2014.
Unfortunately, the lander experienced problems when its system of harpoons (designed to hold it in place) failed to deploy. As a result, it was forced to make another soft landing which left it in a position and location that was not optimal for research. In the future, the ESA could get avoid this by sending a probe to the surface that would deploy the snakes to the surface, which could then burrow into the comet’s interior.
But in the meantime, operations aboard the ISS remain the most realistic and likely application for these robots. Here, astronauts are engaged in ongoing scientific experiments, but are also responsible for maintaining the station and all of its equipment. In this latter respect, the SERPEX project could certainly prove useful, providing them with robot helpers that could help with the regular maintenance.
“It’s possible that a robot could carry out some of the routine inspection and maintenance work,” said Transeth. “The experiments are stacked in the shelf sections, behind which corrosion can occur. To find this out, inspections have to be made. A snake robot could creep behind the sections, carry out an inspection, and perhaps even perform small maintenance tasks.”
Some of the concepts developed by SINTEF so far include the Aiko robot, which was developed to produce a portable system for experimenting with snake robot locomotion. The robot consists of several identical joint modules with two motorized degrees of freedom each. As you can see from the video above, it is propelled by contact forces between the robot and the obstacles in its way.
And then there’s the Wheeko robot, which was developed by SINTEF in conjunction with the Center for Interdisciplinary Research in Space (CIRiS), and the Norwegian Space Center (NSC). Much like Aiko, this experimental robot was designed to study snake robot locomotion across flat surfaces. It consists of ten identical joint modules with two motorized degrees of freedom each.
But of course, developing snake robots that can handle various tasks while working in different environments – ranging from working in micro-gravity aboard the ISS to snaking their way through tunnels on a body with gravity – presents many challenges. And in the coming years, Transeth and his colleagues will be looking for ways to address all of them.
“We want to find out what specifications a snake robot system requires,” he said. “For example, what kind of sensors does the robot need to obtain an adequate understand its surroundings? What technologies are available to help us meet these needs, and what new technologies will have to be developed? What uncertainties are involved in terms to what it may be possible to achieve?”
Already, astronauts aboard the ISS have robotic helpers in the form of the Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES). These free flying satellites serve as test beds for a diverse range of hardware and software, all of which is critical for future space missions that use distributed spacecraft architecture.
Soon enough, they will be replaced by a drone called Astrobee – a robotic cube packed with sensors, cameras, computers, and a propulsion system. The brainchild of the Ames Research Center’s Intelligent Robotics Group, this drone will be flying around the ISS and making inspections.
Some of the technology used by Astrobee will be similar to what Transeth and his colleague are hoping to apply to their snake robot system. As such, they hope to learn much from this drone’s time aboard the ISS and incorporate the lessons that are learned from it.
Artist's Concept of Milky Way vs Galaxy MACS2129-1. Credit: hubblesite.org
Thanks to recent improvements in space-based and ground-based telescopes, astronomers have been able to probe deeper into the Universe than ever before. By looking billions of years back in time, we are able to test our theories about the history of galactic formation and evolution. Unfortunately, studying the very early Universe is a daunting task, and one that is beyond the capabilities of our current instruments.
But by combining the power of the Hubble Space Telescope with a technique known as gravitational lensing, a team of astronomers made the first discovery of a compact galaxy that stopped making stars just a few billion years after the Big Bang. The discovery of such a galaxy existing so early in the Universe is unprecedented and represents a major challenge to \theories of how massive galaxies form and evolve.
Their findings were reported in a study titled “A Massive, Dead Disk Galaxy in the Early Universe“, which appeared in the June 22 issue of the journal Nature. As is indicated in the study, the team relied on data from Hubble which they combined with gravitational lensing – where a massive cluster of galaxies magnifies and stretches images of more distant galaxies beyond them – to study the distant galaxy known as MACS 2129-1.
Image of the Galaxy Cluster MACS J2129-0741, as part of CLASH. Credit: hubblesite.org
What they found was completely unexpected. Given the age of the galaxy – dated to just three billion years after the Big Bang – they expected to see a chaotic ball of stars that were forming due to early galaxies merging. Instead, they noticed that the galaxy, which was disk-shaped (like the Milky Way), was effectively dead – meaning that star formation had already ceased within it.
This was a surprise, seeing as how astronomers did not expect to see this so early in the Universe. What’s more, it was the first time that direct evidence has been obtained that shows how at least some of the earliest “dead” galaxies in the Universe evolved from disk-shaped objects to become the giant elliptical galaxies that we regularly see in the Universe today.
As Sune Toft – a researcher from the Dark Cosmology Center at the Niels Bohr Institute and the lead author on the study – explained, this may force a rethink of how galaxies evolved in the early Universe:
“This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies, Perhaps we have been blind to the fact that early “dead” galaxies could in fact be disks, simply because we haven’t been able to resolve them.”
In previous studies, it was assumed that distant dead galaxies were similar in structure to the local elliptical galaxies they eventually evolved into. Prior to this study, confirmation of this hypothesis was not possible since current instruments are not powerful enough to see that far into space. But by combining the power of gravitational lensing with Hubble’s high resolution, Toft and his team were able to see this dead galaxy clearly.
Galaxy Cluster MACS J2129-0741 and Lensed Galaxy MACS2129- Credit: hubblesite.org
Combining rotational velocity measurements from the ESO’s Very Large Telescope (VLT) with archival data from the Cluster Lensing And Supernova survey with Hubble (CLASH), they were able to determine the size of the galaxy, mass, and age as well as its (defunct) rate of star formation. Ultimately, they found that the remote galaxy is three times as massive as the Milky Way, though only half its size, and is spinning more than twice as fast.
Why this galaxy stopped forming stars is still unknown, and will require follow-up surveys using more sophisticated instruments. But in the meantime, there are some possible theories. For instance, it could be the result of an active galactic nucleus, where a supermassive black hole at the center of MACS 2129-1 inhibited star formation by heating the galaxy’s gas and expelling it from the galaxy.
Or it may be the result of cold gas being streamed into the galaxy’s center where it was rapidly heated and compressed, thereby preventing it from cooling and forming star-forming clouds. But when it comes to how these types of early, dead galaxies could have led to the elliptical galaxies we see today, Toft and his colleagues think they know the answer. As he explained, it could be through mergers:
“If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies. You could also imagine major mergers. This would definitely also destroy the ordered motion of the stars.”
In the coming years, Toft and his team hope to take advantage of the James Webb Telescope (which will be launching in 2018) to search for more early dead galaxies, in the hopes that it can shed light on the unresolved questions this discover raises. And with the ability to probe deeper into space, astronomers anticipate that a great deal more will be revealed about the early Universe.
In the future, derelict satellites could be grappled and removed from key orbits around Earth with a space tug using magnetic forces. Credit: Philippe Ogaki
After 50 years of sending rockets, satellites, and payloads into orbit, humanity has created something of a “space junk” problem. Recent estimates indicate that there are more than 170 million pieces of debris up there, ranging in size from less than 1 cm (0.4 in) to a few meters in diameter. Not only does this junk threaten spacecraft and the ISS, but collisions between bits of debris can cause more to form, a phenomena known as the Kessler Effect.
And thanks to the growth of the commercial aerospace industry and the development of small satellites, things are not likely to get any less cluttered up there anytime soon. Hence why multiple strategies are being explored to clean up the space lanes, ranging from robotic arms and nets to harpoons. But in what may be the most ambitious plan to date, the ESA has proposed creating space tugs with powerful magnets to yank debris out of orbit.
The concept comes from Emilien Fabacher, a researcher from the Institut Supérieur de l’Aéronautique et de l’Espace at the University of Toulouse, France. His concept for a magnetic tug seeks to address one type of space debris in particular – inoperable satellites. These uncontrolled, rapidly spinning objects often weigh up to several tons, and are therefore one of the most significant collision hazards there is.
Illustration showing the problem of space debris. Credit: ESA
When applied to the problem of orbital debris, magnetic attraction is an attractive solutions for the safe deorbiting of spent satellites. For starters, it relies on technology that is standard issue aboard many low-orbiting satellites, which is known as magnetorquers. These electromagnets allow satellites to adjust their orientation using the Earth’s magnetic field. Hence, debris-chasing satellites would not need to be specially equipped in advance.
What’s more, this same magnetic attraction or repulsion technology is being considered as a safe method for allowing multiple satellites to maintain close formations in space. Such satellites – like NASA’s Magnetospheric Multiscale mission (MMS), the Landsat 7 and the Earth Observing-1 satellites, and the ESA’s upcoming LISA mission – are either operational or soon will be around Earth.
Because of this, this kind of magnetic attraction technology presents a safe and effective alternative for deorbiting space junk. As Fabacher explained in a recent ESA press release:
“With a satellite you want to deorbit, it’s much better if you can stay at a safe distance, without needing to come into direct contact and risking damage to both chaser and target satellites. So the idea I’m investigating is to apply magnetic forces either to attract or repel the target satellite, to shift its orbit or deorbit it entirely.”
Artist’s impression of the ESA’s proposed Darwin mission, six formation-flying satellites that would look for exoplanets. Credit: ESA/Medialab
The concept emerged out of a conversation Fabacher had with experts from the ESA’s technical center in the Netherlands. As part of his PhD research, he was looking into how magnetic guidance, navigation and control techniques would work in practice. This led to a discussion about how similar technology could allow swarms of satellites to attract and remove debris from orbit.
After making some calculations that combined a rendezvous simulator with magnetic interaction models, and also taking account the ever-changing state of Earth’s own magnetosphere, Fabacher and his colleagues realized they had a working concept. “The first surprise was that it was indeed possible, theoretically – initially we couldn’t be sure, but it turns out that the physics works fine,” he said.
To break it down, the chaser satellites would generate a strong magnetic field using superconducting wires that are cooled to cryogenic temperatures. These satellites would also rely on magnetic fields to maintain precise flying formations, thus allowing a swarm of chaser satellites the ability to deal with multiple pieces of debris, or to coordinate and guide debris to a specific location.
According to Finn Ankersen – an ESA expert in rendezvous and docking and formation flight – these magnetic tugs would also be able to remove space debris with a very high level of precision. “This kind of contactless magnetic influence would work from about 10–15 meters out, offering positioning precision within 10 cm with attitude precision [of] 1 – 2º,” he said.
Why Space Debris Mitigation is needed. Click for animation. Credit: ESA
The concept is being developed with support provided by the ESA’s Networking/Partnering Initiative, a program that offers support to universities and research institutes for the sake of developing space-related technologies. And it comes at a time when the issue of space debris is becoming increasingly worrisome.
Left unchecked, space debris is likely to become a very serious hazard in the coming years and decades. Already, it is estimated that the small satellite market will grow by $5.3 billion in the next decade (according to Space Works and Eurostat) and many private companies are looking to provide regular launch services to accommodate that growth.
If we intend to begin making a return to the Moon and mounting missions to Mars, we need to make sure the space lanes are clear! And given the importance of the International Space Station to scientific research and international collaboration, and with companies like Bigelow Aerospace looking to establish space habitats in orbit, something has to be done about this problem before it gets completely out of control!
Who knows? Maybe a small fleet or magnetic tugs is just what we need to clean up this mess!
Artist's impression of two merging black holes. Credit: Bohn, Throwe, Hébert, Henriksson, Bunandar, Taylor, Scheel/SXS
The discovery of gravitational waves by the LIGO experiment in 2015 sent ripples through the scientific community. Originally predicted by Einstein’s Theory of General Relativity, the confirmation of these waves (and two subsequent detections) solved a long-standing cosmological mystery. In addition to bending the fabric of space-time, it is now known that gravity can also create perturbations that can be detected billions of light-years away.
Seeking to capitalize on these discoveries and conduct new and exciting research into gravitational waves, the European Space Agency (ESA) recently green-lighted the Laser Interferometer Space Antenna (LISA) mission. Consisting of three satellites that will measure gravitational waves directly through laser interferometry, this mission will be the first space-based gravitational wave detector.
This decision was announced yesterday (Tuesday, June 20th) during a meeting of ESA’s Science Program Committee (SPC). It’s implementation is part of the ESA’s Cosmic Vision plan – the current cycle of the agency’s long-term planning for space science missions – which began in 2015 and will be running until 2025. It is also in keeping with the ESA’s desire to study the “invisible universe“, a policy that was adopted in 2013.
To accomplish this, the three satellites that make up the LISA constellation will be deployed into orbit around Earth. Once there, they will assume a triangular formation – spaced 2.5 million km (1.55 million mi) apart – and follow Earth’s orbit around the Sun. Here, isolated from all external influences but Earth’s gravity, they will then connect to each other by laser and begin looking for minute perturbations in the fabric of space-time.
Much like how the LIGO experiment and other gravitational wave detectors work, the LISA mission will rely on laser interferometry. This process consists of a beam of electromagnetic energy (in this case, a laser) being split in two and then recombined to look for patterns of interference. In LISA’s case, two satellites play the role of reflectors while the remaining one is the both source of the lasers and the observer of the laser beam.
When a gravitational wave passes through the triangle established by the three satellites, the lengths of the two laser beams will vary due to the space-time distortions caused by the wave. By comparing the laser beam frequency in the return beam to the frequency of the sent beam, LISA will be able to measure the level of distortion.
These measurements will have to be extremely precise, since the distortions they are looking for affect the fabric of space-time on the most minuscule of levels – a few millionths of a millionth of a meter over a distance of a million kilometers. Luckily, the technology to detect these waves has already been tested by the LISA Pathfinder mission, which deployed in 2015 and will conclude its mission at the end of the month.
Artist’s concept of the LISA mission. Credit: AEI/Milde Marketing/Exozet
In the coming weeks and months, the ESA will be looking over the design of the LISA mission and completing a cost assessment. If all goes as planned, the mission will be proposed for “adoption” before construction begins and it is expected to be launched by 2034. In the same meeting, the ESA also adopted another important mission that will be searching for exoplanets in the coming years.
This mission is known as the PLAnetary Transits and Oscillations of stars, or PLATO, mission. Like Kepler, this mission will monitor stars within a large sections of the sky to look for small dips in their brightness, which are caused by planets passing between the star and the observer (i.e. the transit method). Originally selected in February of 2014, this mission is now moving from the blueprint phase into construction and will launch in 2026.
It’s an exciting time for the European Space Agency. In recent years, it has committed itself to multiple endeavors in the hope of maintaining Europe’s commitment to and continued presence in space. These include studying the “invisible universe”, mounting missions to the Moon and Mars, maintaining a commitment to the International Space Station, and even building a successor to the ISS on the Moon!
Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
The Kepler space telescope is surely the gift that keeps on giving. After being deployed in 2009, it went on to detect a total of 2,335 confirmed exoplanets and 582 multi-planet systems. Even after two of its reaction wheels failed, it carried on with its K2 mission, which has discovered an additional 520 candidates, 148 of which have been confirmed. And with yet another extension, which will last beyond 2018, it shows no signs of stopping!
In the most recent catalog to be released by the Kepler mission, an additional 219 new planet candidates have been added to its database. More significantly, 10 of these planets were found to be terrestrial (i.e. rocky), of comparable in size to Earth and orbited within their star’s habitable zone – the distance where surface temperatures would be warm enough to support liquid water.
These findings were presented at a news conference on Monday, June 19th, at NASA’s Ames Research Center. Of all the catalogs of Kepler candidates that have been released to date, this one is the most comprehensive and detailed. The eighth in a series of Kepler exoplanet catalogs, this one is based on data that was obtained from the first four years of the mission and is the final catalog that covers the spacecraft’s observations of the Cygnus constellation.
Credits: NASA/Wendy Stenzel
Since 2014, Kepler has ceased looking at a set starfield in the Cygnus constellation and has been collecting data on its second mission – observing fields on the plane of the ecliptic of the Milky Way Galaxy. With the release of this catalog, there are now 4,034 planet candidates that have been identified by Kepler – of which 2,335 have been verified.
An important aspect of this catalog were the methods that were used for producing it, which were the most sophisticated to date. As with all planets detected by Kepler, the latest finds were all made using the transit method. This consists of monitoring stars for occasional dips in brightness, which is used to confirm the presence of planets transiting between the star and the observer.
To ensure that the detections in this latest catalog were real, the team relied on two approaches to eliminate false positives. This consisted of introducing simulated transits into the dataset to make sure the dips that Kepler detected were consistent with planets. Then, they added false signals to see how often the analysis mistook these for planet transits. From this, they were able to tell which planets were overcounted and which were undercounted.
This led to another exciting find, which was the indication that for all of the smaller exoplanets discovered by Kepler, most fell within one of two distinct groupings. Essentially, half the planets that we know of in the galaxy are either rocky in nature and larger than Earth (i.e. Super-Earth’s), or are gas giants that are comparable in size to Neptune (i.e. smaller gas giants).
This conclusion was reached by a team of researchers who used the W.M. Keck Observatory to measure the sizes of 1,300 stars in the Kepler field of view. From this, they were able to determine the radii of 2,000 Kepler planets with extreme precision, and found that there was a clear division between rocky, Earth-sized planets and gaseous planets smaller than Neptune – with few in between.
As Benjamin Fulton, a doctoral candidate at the University of Hawaii in Manoa and the lead author of this study, explained:
“We like to think of this study as classifying planets in the same way that biologists identify new species of animals. Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”
These results are sure to have drastic implications when it comes to knowing the frequency of different types of planets in our galaxy, as well as the study of planet formation. For instance, they noted that most rocky planets discovered by Kepler are up to 75% larger than Earth. And for reasons that are not yet clear, about half of them take on hydrogen and helium, which swells their size to the point that they become almost Neptune-sized.
Histogram shows the number of planets per 100 stars as a function of planet size relative to Earth. Credits: NASA/Ames Research Center/CalTech/University of Hawaii/B.J. Fulton
These findings could similarly have significant implications in the search for habitable planets and extra-terrestrial life. As Mario Perez, Kepler program scientist in the Astrophysics Division of NASA’s Science Mission Directorate, said during the presentation:
“The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth. Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”
From this information, scientists will be able to know with a greater degree of certainty just how many “Earth-like” planets exist within our galaxy. The most recent estimates place the number of planets in the Milky Way at about 100 billion. And based on this data, it would seem that many of these are similar in composition to Earth, albeit larger.
Combined with a statistical models of how many of these can be found within a circumstellar habitable zone, we should have a better idea of just how many potentially-life-bearing worlds are out there. If nothing else, this should simplify some of the math in the Drake Equation!
In the meantime, the Kepler space telescope will continue to make observations of nearby star systems in order to learn more about their exoplanets. This includes the TRAPPIST-1 system and its seven Earth-sized, rocky planets. Its a safe bet that before it is finally retired after 2018, it will have some more surprises in store for us!
Artist's impression of the Demonstrator 3 aerospike test vehicle and the Haas 2CA SSTO rocket. Credit: ARCA
The aerospike engine is a time-honored concept. In the past, NASA tested the concept extensively on the ground and hoped to incorporate it into the Space Shuttle and their next-generation Venture Star program (a Single-Stage-To-Orbit (SSTO) vehicle). However, due to budget constraints, the Space Shuttle ended up being equipped with bell-shaped nozzles instead, and the Venture Star never saw the light of day.
But thanks to New Mexico-based aerospace company ARCA, the aerospike engine is getting a new lease on life. This coming August, they will conduct a test flight of the aerospike engine using their Demonstrator 3 rocket, which will constitute the first space flight of the engine. If all goes well, it will be a major step towards the creation of a fleet of Single-Stage-To-Orbit (SSTO) rockets.
What makes the aerospike engine appealing is the fact that it offers efficient thrust over a wide range of altitudes, and is also more fuel-efficient than current engines. With traditional bell-shaped nozzles, reliable thrust tends to occur only at sea level. Beyond that, the engine isn’t capable of taking advantage of decreases in atmospheric pressure since the gases are contained by the nozzle.
The test of twin Linear Aerospike XRS-2200 engines, originally built for the X-33 program, was performed on August 6, 2001 at NASA’s Sternis Space Center, Mississippi. Credit: NASA’s Marshall Space Flight Center
In contrast, the aerospike engine’s exhaust is capable of expanding from sea level all the way up to space, which ensures both fuel-efficiency and a high degree of specific impulse (Isp) at all flight levels. Already, ARCA and NASA have scheduled ground and vacuum tests for the engine. But in the meantime, they also want to gather data on how it performs in flight. This is where the Demonstrator 3 test comes into play.
In addition to testing the engine’s efficiency, it will also test the aerospike’s super-cold fuel storage technology. Basically, the engine relies on a decomposing 70% concentration of hydrogen peroxide at a temperature of only 250 °C to generate thrust. The byproduct of this is oxygen and water, which makes the aerospike the most environmentally-friendly rocket concept to date. As Dumitru Popescu, the CEO of ARCA, said in a recent statement:
“By sending the Demonstrator 3 rocket in space using a super cold engine, with only 250 °C instead of 3500 °C in the reaction chamber, paired with the aerospike technology, we are going to demonstrate the impressive potential of the aerospike.”
Ultimately, the goal here is to demonstrate that SSTO rockets are feasible, which ARCA is exploring with their Haas 2CA concept. The latest in the Haas rocket family, named in honor of Austrian-Romanian rocketry pioneer Conrad Haas, this launch vehicle uses hydrogen peroxide and kerosene for fuel and is capable of generating 22,900 kg (50,500 lbs) of thrust at sea level, and about 33,565 kg (74,000 lbs) in a vacuum.
Compared to multi-stage rockets, SSTOs offer both lower costs and greater flexibility when it comes to launching small payloads into orbit. According to estimates produced by Space Works and Eurostat, this small satellite market will be growing by $5.3 billion in the next decade. As such, aerospace companies that can offer competitive launch rates and flexibility will be able to take advantage of this growth.
The company unveiled the Haas 2CA back in March of 2017 at their company headquarters in Las Cruces, New Mexico. In 2018, ARCA hopes to conduct their first test launch of the Haas 2CA from NASA’s Wallops Flight Facility in Virginia. But before that can happen, the company needs to make sure the aerospike engine performs as well as expected. As Popescu explained:
“The Haas 2CA Single Stage to Orbit is just the beginning of a new generation of space vehicle, shaped by innovation that will generate lower cost. We are going to answer one of the industry’s most asked questions: can an aerospike deliver in flight the pressure compensation generated by altitude variation and deliver the expected performance by saving fuel? We want to pick up where NASA left off and prove that this technology is actually the way to go for space flights.”
The test flight, which will take place at Spaceport America in the New Mexico desert, will consist of a suborbital space flight that will take the Demonstrator 3 up to an altitude of 100 km. If this flight is achieved, ARCA will have demonstrated that the engine technology is flight qualified, that SSTO rockets are feasible, and that super cold engines paired with aerospike technology will allow for environmentally friendly suborbital rockets.
Artist’s impression of the Haas 2C rocket ascending into orbit. Credit: ARCA
The test will also be a milestone for the commercial aerospace industry, which was founded on the desires to make space more accessible and lowering the costs associated with individual launches. And as Popescu was sure to indicate, the best way to do this is not to merely improve upon existing concepts, but leverage cutting-edge and time-tested technologies to create new ones.
“We are confident that the aerospike engine combined with composite material fuel tanks and dense fuels will significantly lower the costs for orbital and suborbital launches,” he said. “We truly believe that the answer for cost reduction of space flight is innovation, not trying to make old technologies a little bit more efficient. This will never generate significant price drop of space launches, but merely small improvements. With this philosophy in mind we expect to increase the registered value of our company from its current $20 million to at least $200 millions by 2019.”
The development of SSTOs are just one way that the commercial aerospace industry is making space exploration more economical. Other examples include SpaceX’s developments of reusable rockets, and Rocketlab‘s use of lightweight materials to create two-stage disposable rockets.
These measures are not only allowing for the commercialization of Low-Earth Orbit (LEO), but are opening up possibilities that were previously thought to be impossible for the time being – like space-based solar power and space habitats!
Stay tuned for more on this and other upcoming tests. And be sure to check out this video on how ARCA is preparing for the upcoming aerospike test flight, courtesy of ARCA:
Artist's impression of the the Interplanetary Spacecraft approaching Mars. Credit: SpaceX
Elon Musk has never been one to keep his long-term plans to himself. Beyond the development of reusable rockets, electric cars, and revolutionizing solar power, he has also been quite vocal about establishing a colony on Mars within his lifetime. The goal here is nothing less than ensuring the survival of the human race by creating a “backup location”, and calls for some serious planning and architecture.
The paper was produced by Scott Hubbard, a consulting professor at Stanford University and the Editor-in-Chief of NewSpace, and includes all the material and slides from Musk’s original presentation. Contained within are Musk’s thoughts on how the colonization of Mars could be accomplished in this century and what issues would need to be addressed.
Elon Musk revealing his Mars Plans at the 67th annual meetings of the IAC. Credit: SpaceX/IAC
These include the costs of sending people and payloads to Mars, the technical details of the rocket and vehicle that would be making the trip, and possible cost breakdowns and timelines. But of course, he also addresses the key philosophical questions – “Why go?” and “Why Mars?”
Addressing this first question is one of the most important aspects of space exploration. Remember John F. Kennedy’s iconic “We Choose to go to the Moon” speech? Far from just being a declaration of intent, this speech was a justification by the Kennedy administration for all the time, energy, and money it was committing to the Apollo program. As such, Kennedy’s speech stressed above all else why the goal was a noble undertaking.
In looking to Mars, Musk struck a similar tone, emphasizing survival and humanity’s need to expand into space. As he stated:
“I think there are really two fundamental paths. History is going to bifurcate along two directions. One path is we stay on Earth forever, and then there will be some eventual extinction event. I do not have an immediate doomsday prophecy, but eventually, history suggests, there will be some doomsday event. The alternative is to become a space-bearing civilization and a multi-planetary species, which I hope you would agree is the right way to go.”
As for what makes Mars the natural choice, that was a bit more of a tough sell. Granted, Mars has a lot of similarities with Earth – hence why it is often called “Earth’s Twin” – which makes it a tantalizing target for scientific research. But it also has some rather stark differences that make long-term stays on the surface seem less than appealing. So why would it be the natural choice?
Artist’s rendition of a passenger aboard the ITS looking down on Mars. Credit: SpaceX
As Musk explains, proximity has a lot to do with it. Sure, Venus is closer to Earth, getting as close as 41 million km (25,476,219 mi), compared to 56 million km (3,4796,787 mi) with Mars. But Venus’ hostile environment is well-documented, and include a super-dense atmosphere, temperatures hot enough to melt lead and sulfuric acid rain! Mercury is too hot and airless, and the Jovian moons are very far.
This leaves us with just two options for the near-future, as far as Musk is concerned. One is the Moon, which is likely to have a permanent settlement on it in the coming years. In fact, between the ESA, NASA, Roscosmos, and the Chines National Space Administration, there is no shortage of plans to build a lunar outpost, which will serve as a successor to the ISS.
But compared to Mars, it is less resource rich, has no atmosphere, and represents a major transition as far as gravity (0.165 g compared to 0.376 g) and length of day (28 days vs. 24.5 hours) are concerned. Herein lies the greatest reason to go to Mars, which is the fact that our options are limited and Mars is the most Earth-like of all the bodies that are currently accessible to us.
What’s more, Musk makes allowances for the fact that colonists could start kick-starting the terraforming process, to make it even more Earth-like over time. As he states (bold added for emphasis):
“In fact, we now believe that early Mars was a lot like Earth. In effect, if we could warm Mars up, we would once again have a thick atmosphere and liquid oceans. Mars is about half as far again from the Sun as Earth is, so it still has decent sunlight. It is a little cold, but we can warm it up. It has a very helpful atmosphere, which, being primarily CO2 with some nitrogen and argon and a few other trace elements, means that we can grow plants on Mars just by compressing the atmosphere.
“It would be quite fun to be on Mars because you would have gravity that is about 37% of that of Earth, so you would be able to lift heavy things and bound around. Furthermore, the day is remarkably close to that of Earth. We just need to change the populations because currently we have seven billion people on Earth and none on Mars.”
Naturally, no mission can be expected to happen without the all-important vehicle. To this end, Musk used the annual IAC meeting to unveil his company’s plans for the Interplanetary Transport System. An updated version of the Mars Colonial Transporter (which Musk began talking about in 2012), the ITS will consist of two main components – a reusable rocket booster and the Interplanetary Spaceship.
The process for getting to Mars with these components involves a few steps. First, the rocket booster and spaceship take off together and the spaceship is delivered into orbit. Next, while the spaceship assumes a parking orbit, the booster returns to Earth to be reloaded with the tanker craft. This vehicle is the same design as the spaceship, but contains propellant tanks instead of cargo areas.
The tanker is then launched into orbit with the booster, where it will rendezvous with the spaceship and refuel it for the journey to Mars. Overall, the propellant tanker will go up anywhere from three to five times to fill the tanks of the spacecraft while it is in orbit. Musk estimates that the turnaround time between the spacecraft launch and the booster retrieval could eventually be as low as 20 minutes.
This process (if Musk gets its way) would expand to include multiple spaceships making the journey to and from Mars every 26 months (when Mars and Earth are closest together):
“You would ultimately have upwards of 1,000 or more spaceships waiting in orbit. Hence, the Mars Colonial fleet would depart en masse. It makes sense to load the spaceships into orbit because you have got 2 years to do so, and then you can make frequent use of the booster and the tanker to get really heavy reuse out of those. With the spaceship, you get less reuse because you have to consider how long it is going to last—maybe 30 years, which might be perhaps 12–15 flights of the spaceship at most.”
In terms of the rocket’s structure, it would consist of an advanced carbon fiber exterior surrounding fuel tanks, which would rely on an autogenous pressurization system. This involves the fuel and oxygen being gasified through heat exchanges in the engine, which would then be used to pressurize the tanks. This is a much simpler system than what is currently being used for the Falcon 9 rocket.
The booster would use 42 Raptor engines arranged in concentric rings to generate thrust. With 21 engines in the outer ring, 14 in the inner ring, and seven in a center cluster, the booster would have an estimated lift-off thrust of 11,793 metric tons (13,000 tons) – 128 MegaNewtons – and a vacuum thrust of 12,714 metric tons (14,015 tons), or 138 MN. This would make it the first spacecraft where the rocket performance bar exceeds the physical size of the rocket.
As for the spacecraft, the designs calls for a pressurized section at the top with an unpressurized section beneath. The pressurized section would hold up to 100 passengers (thought Musk hopes to eventually increase that capacity to 200 people per trip), while all the luggage and cargo necessary for building the Martian colony would be kept in the unpressurized section below.
As for the crew compartments themselves, Musk was sure to illustrate how time in them would not be boring, since the transit time is a long. “Therefore, the crew compartment or the occupant compartment is set up so that you can do zero-gravity games – you can float around,” he said. “There will be movies, lecture halls, cabins, and a restaurant. It will be really fun to go. You are going to have a great time!”
The system architecture of the Interplanetary Transport System. Credit: SpaceX
Below both these sections, the liquid oxygen tank, fuel tank and spacecraft engines are located. The engines, which would be directly attached to the thrust cone at the base, would consists of an outer ring of three sea-level engines – which would generate 361 seconds of specific impulse (Isp) – and an inner cluster of six vacuum engines that would generate 382s Isp.
The exterior of the spacecraft will also be fitted with a heatshield, which will be composed of the same material that SpaceX uses on its Dragon spacecraft. This is known as a phenolic-impregnated carbon ablator (PICA), which SpaceX is on their third version of. In total, Musk estimates that the Interplanetary Spaceship will be able to transport 450 tons of cargo to Mars, depending upon how many times the tanker can refill the craft.
And, depending on the Earth-Mars rendezvous, the transit time could be as little as 80 days one-way (figuring for a speed of 6km/s). But with time, Musk hopes to cut that down to just 30 days, which would make it possible to establish a sizable population on Mars in a relatively short amount of time. As Musk indicated, the magic number here in 1 million, meaning the number of people it would take to establish a self-sustaining colony on Mars.
He admitted that this would be a major challenge, and could as long as a century to complete:
“If you can only go every 2 years and if you have 100 people per ship, that is 10,000 trips. Therefore, at least 100 people per trip is the right order of magnitude, and we may end up expanding the crew section and ultimately taking more like 200 or more people per flight in order to reduce the cost per person. However, 10,000 flights is a lot of flights, so ultimately you would really want in the order of 1,000 ships. It would take a while to build up to 1,000 ships. How long it would take to reach that million-person threshold, from the point at which the first ship goes to Mars would probably be somewhere between 20 and 50 total Mars rendezvous—so it would take 40–100 years to achieve a fully self-sustaining civilization on Mars.”
Cutaway of the Interplanetary Spaceship. Credit: SpaceX
When the ITS is ready to launch, it will do so from Launch Pad 39A at the Kennedy Space Center in Florida, which SpaceX currently uses to conduct Falcon 9 launches from. But of course, the most daunting aspect of any colonization effort is cost. At present, and using current methods, sending upwards of 1 million people to Mars is simply not affordable.
Using Apollo-era methods as a touchstone, Musk indicated that the cost to go to Mars would be around $10 billion per person – which is derived from the fact that the program itself cost between $100 and $200 billion (adjust for inflation) and resulted in 12 astronauts setting foot on the Moon. Naturally, this is far too high for the sake of creating a self-sustaining colony with a population of 1 million.
As a result, Musk claimed that the cost of transporting people to Mars would have to be cut by a whopping 5 million percent! Musk’s desire to lower the costs associated with space launches is well-known, and is the very reason he founded SpaceX and began developing reusable technology. However, costs would need to be lowered to the point where a ticket to Mars would cost about the same as a median house – i.e. $200,000 – before any trips to Mars could happen.
Artist’s impression of the ITS in transit, with its solar arrays deployed. Credit: SpsaceX
As to how this could be done, several strategies are outlined, many of which Musk and space agencies like NASA are already actively pursuing. They include full Reusability, where all stages of a rocket and its cargo module (not just the first stage) would have to be retrievable and reusable. Refueling in Orbit is a second means, which would mean the spacecraft would not have to carry all the fuel they need with them from Earth.
On top of that, there would have to be the option for propellant Production on Mars, where the spaceship will be able to refuel at Mars to make the return trip. This concept has been explored in the past for lunar and Martian missions. And in Mars’ case, the presence of atmospheric and frozen CO², and water in both the soil and the polar ice caps, would mean that methane, oxygen and hydrogen fuel could all be manufactured.
Lastly, there is the question of which propellant would be best. As it stands, there are there basic choices when it comes – kerosene (rocket fuel), hydrogen, and methane. All of these present certain advantages and can be manufactured in-situ on Mars. But based on a cost-benefit breakdown, Musk claims that methane would be the most cost-effective propellant.
As always, Musk also raised the issue of timelines and next steps. This consisted of a rundown of SpaceX’s accomplishments over the past decade and a half, followed by an outline of what he hopes to see his company do in the coming years and decades.
Artist impression of a Mars settlement with cutaway view. Credit: NASA Ames Research Center
These include the development of the first Interplanetary Spaceship in about four years time, which will be followed by suborbital test flights. He even hinted how the spacecraft could have commercial applications, being used for the rapid transportation of cargo around the world. As for the development of the booster, he indicated that this would be a relatively straightforward process since it simply involves scaling up the existing Falcon 9 booster.
Beyond that, he estimated that (assuming all goes well) a ten-year time frame would suffice for putting all the components together so that it would work for bringing people to Mars. Last, but not least, he offered some glimpses of what could be accomplished with ITS beyond Mars. As the name suggests, Musk is hoping to conduct missions to other destination in the Solar System someday.
Given the opportunities for in-situ fuel production (thanks to the abundance of water ice), the moons of both Jupiter and Saturn were mentioned as possible destination. But beyond moons like Europa, Enceladus, and Titan (all of which were mentioned), even destinations in the trans-Neptunian region of the Solar System were indicated as a possibility.
Given that Pluto also has an abundance of water ice on its surface, Musk claimed that a refueling depot could be built here to service missions to the Kuiper Belt and Oort Cloud. “I would not recommend this for interstellar journeys,” he admitted, “but this basic system—provided we have filling stations along the way—means full access to the entire greater solar system.”
Artist’s impression of the ITS conducting a flyby of Jupiter. Credit: SpaceX
The publication of this paper, many months after Musk presented the details of his plan to the annual IAC meeting, has naturally generated both approval and skepticism. While there are those who would question Musk’s timelines and his ability to deliver on the proposals contained within, others see it as a crucial step in the fulfillment of Musk’s long-held desire to see the colonization of Mars happen in this century.
To Scott Hubbard, it serves as a valuable contribution to the history of space exploration, something that future generations will be able to access so they can chart the history of Mars exploration – much in the same way NASA archival materials are used to study the history of the Moon landing. As he remarked:
“In my view, publishing this paper provides not only an opportunity for the spacefaring community to read the SpaceX vision in print with all the charts in context, but also serves as a valuable archival reference for future studies and planning. My goal is to make New Space the forum for publication of novel exploration concepts-particularly those that suggest an entrepreneurial path for humans traveling to deep space.”
Elon Musk is no stranger to thinking big and dreaming big. And while many of his proposals in the past did not come about in the time frame he originally specified, no one can doubt that he’s delivered so far. It will be very exciting to see if he can take the company he founded 15 years ago for the sake of fostering the exploration of Mars, and use it instead to lead a colonization effort!
Update: Musk tweeted his thanks to Hubbard for the publication and has indicated that there are some “major changes to the plan coming soon.”
And be sure to check out this video of Musk’s full speech at the 67th annual meeting of the IAC, courtesy of SpaceX:
Artist's impression of a brown dwarf orbiting a white dwarf star. Credit: ESO
Death is simply a part of life, and this is no less the case where stars and other astronomical objects are concerned. Sure, the timelines are much, much greater where these are concerned, but the basic rule is the same. Much like all living organism, stars eventually reach old age and become white dwarfs. And some are not even fortunate enough to be born, instead becoming a class of failed stars known as brown dwarfs.
Despite being familiar with these objects, astronomers were certainly not expecting to find examples of both in a single star system! And yet, according to a new study, that is precisely what an international team of astronomers discovered when looked at WD 1202-024. Using data from the Kepler space telescope, they spotted a binary system consisting of a failed star (a brown dwarf) and the remnant of a star (a white dwarf).
Stardust in the Perseus Molecular Cloud, a star-forming region in the Perseus constellation. Credit & Copyright: Lorand Fenyes
For us Earthlings, life under a single Sun is just the way it is. But with the development of modern astronomy, we’ve become aware of the fact that the Universe is filled with binary and even triple star systems. Hence, if life does exist on planets beyond our Solar System, much of it could be accustomed to growing up under two or even three suns. For centuries, astronomers have wondered why this difference exists and how star systems came to be.
Whereas some astronomers argue that individual stars formed and acquired companions over time, others have suggested that systems began with multiple stars and lost their companions over time. According to a new study by a team from UC Berkeley and the Harvard-Smithsonian Center for Astrophysics (CfA), it appears that the Solar System (and other Sun-like stars) may have started out as binary system billions of years ago.
This study, titled “Embedded Binaries and Their Dense Cores“, was recently accepted for publication in the Monthly Notices of the Royal Astronomical Society. In it, Sarah I. Sadavoy – a radio astronomer from the Max Planck Institute for Astronomy and the CfA – and Steven W. Stahler (a theoretical physicist from UC Berkeley) explain how a radio surveys of a star nursery led them to conclude that most Sun-like stars began as binaries.
The dark molecular cloud, Barnard 68, is a stellar nursery that can only be studied using radio astronomy. Credit: FORS Team, 8.2-meter VLT Antu, ESO
For several decades, astronomers have known that stars are born inside “stellar nurseries”, which are the dense cores that exist within immense clouds of dust and cold, molecular hydrogen. These clouds look like holes in the star field when viewed through an optical telescope, thanks to all the dust grains that obscure light coming from the stars forming within them and from background stars.
Radio surveys are the only way to probe these star-forming regions, since the dust grains emit radio transmissions and also do not block them. For years, Stahler has been attempting to get radio astronomers to examine molecular clouds in the hope of gathering information on the formation of young stars inside them. To this end, he approached Sarah Sadavoy – a member of the VANDAM team – and proposed a collaboration.
The two began their work together by conducting new observations of both single and binary stars within the dense core regions of the Perseus cloud. As Sadavoy explained in a Berkeley News press release, the duo were looking for clues as to whether young stars formed as individuals or in pairs:
“The idea that many stars form with a companion has been suggested before, but the question is: how many? Based on our simple model, we say that nearly all stars form with a companion. The Perseus cloud is generally considered a typical low-mass star-forming region, but our model needs to be checked in other clouds.”
Infrared image from the Hubble Space Telescope, showing a bright, fan-shaped object (lower right quadrant) thought to be a binary star that emits light pulses as the two stars interact. Credit: NASA/ESA/ J. Muzerolle (STScI)
Their observations of the Perseus cloud revealed a series of Class 0 and Class I stars – those that are <500,000 old and 500,000 to 1 million years old, respectively – that were surrounded by egg-shaped cocoons. These observations were then combined with the results from VANDAM and other surveys of star forming regions – including the Gould Belt Survey and data gathered by SCUBA-2 instrument on the James Clerk Maxwell Telescope in Hawaii.
From this, they created a census of stars within the Perseus cloud, which included 55 young stars in 24 multiple-star systems (all but five of them binary) and 45 single-star systems. What they observed was that all of the widely separated binary systems – separated by more than 500 AU – were very young systems containing two Class 0 stars that tended to be aligned with the long axis of their egg-shaped dense cores.
Meanwhile, the slightly older Class I binary stars were closer together (separated by about 200 AU) and did not have the same tendency as far as their alignment was concerned. From this, the study’s authors began mathematically modelling multiple scenarios to explain this distribution, and concluded that all stars with masses comparable to our Sun start off as wide Class 0 binaries. They further concluded that 60% of these split up over time while the rest shrink to form tight binaries.
“As the egg contracts, the densest part of the egg will be toward the middle, and that forms two concentrations of density along the middle axis,” said Stahler. “These centers of higher density at some point collapse in on themselves because of their self-gravity to form Class 0 stars. “Within our picture, single low-mass, sunlike stars are not primordial. They are the result of the breakup of binaries. ”
The two brightest stars of the Centaurus constellation, the binary star system of Alpha Centauri. Credit: Wikipedia Commons/Skatebiker
Findings of this nature have never before been seen or tested. They also imply that each dense core within a stellar nursery (i.e. the egg-shaped cocoons, which typically comprise a few solar masses) converts twice as much material into stars as was previously thought. As Stahler remarked:
“The key here is that no one looked before in a systematic way at the relation of real young stars to the clouds that spawn them. Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution. We now believe that most stars, which are quite similar to our own sun, form as binaries. I think we have the strongest evidence to date for such an assertion.”
This new data could also be the start of a new trend, where astronomers rely on radio telescopes to examine dense star-forming regions with the hopes of witnessing more in the way of stellar formations. With the recent upgrades to the VLA and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the ongoing data provided by the SCUBA-2 survey in Hawaii, these studies may be coming sooner other than later.
Another interesting implication of the study has to do with something known as the “Nemesis hypothesis”. In the past, astronomers have conjectured that a companion star named “Nemesis” existed within our Solar System. This star was so-named because the theory held that it was responsible for kicking the asteroid which caused the extinction of the dinosaurs into Earth’s orbit. Alas, all attempts to find Nemesis ended in failure.
Artist’s impression of the binary star system of Sirius, a white dwarf star in orbit around Sirius (a white supergiant). Credit: NASA, ESA and G. Bacon (STScI)
As Steven Stahler indicated, these findings could be interpreted as a new take on the Nemesis theory:
“We are saying, yes, there probably was a Nemesis, a long time ago. We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years.”
So while their results do not point towards a star being around for the extinction of the dinosaurs, it is possible (and even highly plausible) that billions of years ago, the Solar planets orbited around two stars. One can only imagine what implications this could have for the early history of the Solar System and how it might have affected planetary formation. But that will be the subject of future studies, no doubt!
