The MASCam team behind the MASCOT rover's camera identified two types of rock on Ryugu: Type 1 are dark, irregularly-shaped boulders with crumpled, cauliflower-like surfaces. Type 2 are brighter, with sharp edges, and smooth, fractured surfaces. Image Credit: MASCOT/DLR/JAXA
When Japan’s Hayabusa 2 spacecraft arrived at asteroid Ryugu in June 2018, it carried four small rovers with it. Hayabusa 2 is primarily a sample-return mission, but JAXA (Japan Aerospace Exploration Agency) sent rovers along to explore the asteroid’s surface and learn as much as they could from their visit. There’s also no guarantee that the sample return will be successful.
They chose Ryugu because the asteroid is classified as a primitive carbonaceous asteroid. This type of asteroid is a desirable target because it represents the primordial matter that formed the bodies in our Solar System. It’s also pretty close to Earth.
The sample from Ryugu, which will make it to Earth in December 2020, is the big science prize from this mission. Analyzing it in Earth-based laboratories will tell us a lot more than spacecraft instruments can. But the rovers that landed on Ryugu’s surface have already revealed a lot about Ryugu.
Detailed view of the rubble-pile asteroid 25143 Itokawa visited by the Japanese spacecraft Hayabusa in 2005. Credit: JAXA
Right now, the Japanese Aerospace Exploration Agency‘s (JAXA) Hayabusa2 spacecraft is busy exploring the asteroid 162173 Ryugu. Like it’s predecessor, this consists of a sample-return mission, where regolith from the asteroid’s surface will be brought back home for analysis. In addition to telling us more about the early Solar System, these studies are expected to shed light on the origin of Earth’s water (and maybe even life).
Meanwhile, scientists here at home have been busy examining the samples returned from 25143 Itokawa by the Hayabusa1spacecraft. Thanks to a recent study by a pair of cosmochemists from Arizona State University (ASU), it is now known that this asteroid contained abundant amounts of water. From this, the team estimates that up to half the water on Earth could have come from asteroid and comet impacts billions of years ago.
The asteroid Bennu, as imaged by OSIRIS-REx from a distance of about 80 km. Image Credit: NASA/University of Arizona
NASA’s OSIRIS-REx spacecraft has reached its destination and is now in orbit around asteroid Bennu. The spacecraft travelled for over two years and covered more than 2 billion kms. It will spend a year in orbit, surveying the surface of the Potentially Hazardous Object (PHO) before settling on a location for the key phase of its mission: a sample return to Earth.
Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) telescope in Hawaii announced the first-ever detection of an interstellar asteroid – I/2017 U1 (aka. ‘Oumuamua). Since that time, no effort has been spared to study this object before it leaves our Solar System. These include listening to it for signs of communications, determining its true nature and shape, and determining where it came from.
In fact, the question of this interstellar object’s origins has been mystery since it was first discovered. While astronomers are sure that it came from the direction of Vega and some details have been learned about its past, where it originated from remains unknown. But according to a new study by a team of astronomers from the University of Toronto, Scarborough, ‘Oumuamua may have originally come from a binary star system.
Oumuamua as it appeared using the William Herschel Telescope on the night of October 29. Credit: Queen’s University Belfast/William Herschel Telescope
For the sake of their study, Jackson and his co-authors considered how in single star systems (like our own), asteroids do not get ejected very often. For the most part, it is comets that become interstellar objects, mainly because they orbit the Sun at a greater distance and are less tightly bound by its gravity. And while ‘Oumuamua was initially mistaken for a comet, follow-up observations by the European Southern Observatory (ESO) indicated that it is likely an asteroid.
With the help of other astronomers, it soon became apparent that ‘Oumuamua was likely an oddly-shaped rocky object that measured about 400 meters (1312 ft) long and was tube-shaped. These findings were rather surprising to astronomers. As Jackson explained in a recent Royal Astronomical Society press release:
“It’s really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the Solar System ejects many more comets than asteroids.”
As such, Jackson and his team hypothesized that interstellar objects like ‘Oumuamau are more likely to be ejected from a binary system. To test this theory, they constructed a population synthesis model that considered just how common binary star systems are in the Galaxy. They also conducted 2000 N-body simulations to see just how efficient such systems would be at ejecting objects like ‘Oumuamua.
Diagram showing the orbit of the interstellar asteroid ‘Oumuamua as it passes through the Solar System. Credit: ESO/K. Meech et al.
What they found was that binary stars are produced at a rate of about 30% by number and 41% by mass, and that rocky objects like ‘Oumuamua are far more likely to be ejected from binary than single star systems. Based on ‘Oumuamua’s rocky composition, they also determined that the asteroid was likely ejected from the inner part of its solar system (i.e. inside the “Ice Line”) while the system was still in the process of formation.
Lastly, they determined that rocky objects are ejected from binary systems in comparable numbers to icy objects. This is based on the fact that the presence of a companion star would mean that more material would become unstable due to stellar encounters. In the end, this material would be more likely to be ejected rather than accreted to form planets, or take up residence in the outer reaches of the star system.
While there are still many unanswered questions about ‘Oumuamua, it remains the first interstellar asteroid that scientists have ever known. As such, its continued study can tell us a great deal about what lies beyond our Solar System. As Jackson put it:
“The same way we use comets to better understand planet formation in our own Solar System, maybe this curious object can tell us more about how planets form in other systems.”
Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser
Back in October, the announcement of the first interstellar asteroid triggered a flurry of excitement. Since that time, astronomers have conducted follow-up observations of the object known as 1I/2017 U1 (aka. `Oumuamua) and noted some rather interesting things about it. For example, from rapid changes in its brightness, it has been determined that the asteroid is rocky and metallic, and rather oddly-shaped.
Observations of the asteroid’s orbit have also revealed that it made its closest pass to our Sun back in September of 2017, and it is currently on its way back to interstellar space. Because of the mysteries this body holds, there are those who are advocating that it be intercepted and explored. One such group is Project Lyra, which recently released a study detailing the challenges and benefits such a mission would present. Continue reading “Project Lyra, a Mission to Chase Down that Interstellar Asteroid”
Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) telescope in Hawaii picked up the first interstellar asteroid, named 1I/2017 U1 (aka. `Oumuamua). After originally being mistaken for a comet, observations performed by the European Southern Observatory (ESO) and other astronomers indicated that it was actually an asteroid that measures about 400 meters (1312 ft) long.
Thanks to data obtained by the ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile, the brightness, color and orbit of this asteroid have been precisely determined. And according to a new study led by Dr. Karen Meech of the Institute for Astronomy in Hawaii, `Oumuamua is unlike any other asteroid we’ve ever seen, in that its shape is highly elongated (i.e. very long and thin).
The VLT was intrinsic to the combined effort to characterize the fast-moving asteroid rapidly, as it needed to be observed before it passed back into interstellar space again. Based on initial calculations of `Oumuamua’s orbit, astronomers had determined that it had already passed the closest point in its orbit to the Sun in September of 2017. Together with other large telescopes, the VLT captured images of the asteroid using its FORS instrument.
What these revealed was that `Oumuamua varies dramatically in terms of brightness (by a factor of ten) as it spins on its axis every 7.3 hours. As Dr. Meech explained in an ESO press release, this was both surprising and highly significant:
“This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”
These observations also allowed Dr. Meech and her team to constrain Oumuamua’s composition and basic properties. Essentially, the asteroid is now believed to be a dense and rocky asteroid with a high metal content and little in the way of water ice. It’s dark and reddened surface is also an indication of tholins, which are the result of organic molecules (like methane) being irradiated by cosmic rays for millions of years.
Unlike other asteroids that have been studied in Near-Earth space and the Solar System at large, `Oumuamua is unique in that it is not bound by the Sun’s gravity. In addition to originating outside of our Solar System, its hyperbolic orbit – which has an eccentricity of 1.2 – means that it will head back out into interstellar space after its brief encounter with our Solar System.
Based on preliminary calculations of its orbit, astronomers have deduced that it came from the general direction of Vega, the brightest star in the northern constellation of Lyra. Traveling at a whopping speed of 95,000 km/hour (59,000 mph), `Oumuamua would have left the Vega system about 300,000 years ago. However, it is also possible that the asteroid may have originated somewhere else entirely, wandering the Milky Way for millions of years.
Astronomers estimate that interstellar asteroids like `Oumuamua pass through the inner Solar System at a rate of about once a year. But until now, they have been too faint and difficult to detect in visible light, and have therefore gone unnoticed. It is only recently that survey telescopes like Pan-STARRS have been powerful enough to have a chance at detecting them.
Hence what makes this discovery so significant in the first place. As the first asteroid of its kind to be detected, further improvements in our instruments will it make it easier to spot the others that are sure to be on the way. And as Olivier Hainaut – a researcher with the ESO and a co-author on the study – indicated, there’s plenty more to be learned from `Oumuamua as well:
“We are continuing to observe this unique object, and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy,” he said. “And now that we have found the first interstellar rock, we are getting ready for the next ones!”
And be sure to enjoy this ESOcast video about `Oumuamua, courtesy of the ESO:
Artist's concept of a large asteroid passing by the Earth-Moon system. Credit: A combination of ESO/NASA images courtesy of Jason Major/Lights in the Dark.
Beyond the Earth-Moon system, thousands of asteroids known as Near-Earth Objects (NEOs) are known to exist. These rocks periodically cross Earth’s orbit and make close a flyby of Earth. Over the course of millions of years, some even collide with the Earth, causing mass extinctions. Little wonder then why NASA’s Center for Near Earth Object Studies (CNEOS) is dedicated to monitoring the larger objects that occasionally come close to our planet.
One of these objects is 2012 TC4, a small and oblong-shaped NEO that was first spotted in 2012 during a close flyby of Earth. During its most recent flyby – which took place on Thursday, October 12th,2017 – an international team of astronomers led by NASA scientists used the opportunity to conduct the first international exercise to test global responses to an impending asteroid strike.
This exercise was known as the “TC4 Observation Campaign“, which began this past July and concluded with the asteroid flyby. It all began when astronomers at the European Southern Observatory’s (ESO) Paranal Observatory in Chile used the Very Large Telescope (VLT) to recover 2012 TC4. When the asteroid made its final close approach to Earth in mid-October, it passed Earth by at a distance of 43,780 km (27,200 mi).
Diagram showing 2012 TC4’s heliocentric orbit, which has changed due to the 2012 and 2017 close encounters with Earth. Credit: NASA/JPL-Caltech
The goal of this exercise was simple: recover, track and characterize a real asteroid as if it were likely to collide with Earth. In addition, the exercise was an opportunity to test the International Asteroid Warning Network, which conducts observations of potentially hazardous asteroids, attempts to model their behavior, make predictions, and share these findings with institutions around the world.
On Oct. 12th, TC4 flew by Earth at roughly 0.11 times the distance between Earth and the Moon. In the months leading up to the flyby, astronomers from the US, Canada, Columbia, Germany, Israel, Italy, Japan, the Netherlands, Russia and South Africa tracked TC4 from the ground. At the same time, space-based telescopes studied the asteroid’s orbit, shape, rotation and composition.
Detlef Koschny is the co-manager of the Near-Earth Object segment in the European Space Agency (ESA)’s Space Situational Awareness program. As he was quoted in a recent NASA press release:
“This campaign was an excellent test of a real threat case. I learned that in many cases we are already well-prepared; communication and the openness of the community was fantastic. I personally was not prepared enough for the high response from the public and media – I was positively surprised by that! It shows that what we are doing is relevant.”
Asteroid 2012 TC4 appears as a dot at the center of this composite of 37 individual 50-second exposures obtained on Aug. 6, 2017 by the European Southern Observatory’s Very Large Telescope. Credit: NASA/JPL-Caltech
Based on their observations, scientists at CNEOS – which is located at the Jet Propulsion Laboratory in Pasadena, California – were able to determine all the necessary characteristics of TC4. This included its precise orbit, the distance it would pass by Earth on Oct. 12th, and discern if there was any possibility of a future impact. As Davide Farnocchia, a member of CNEOS who led the effort to determine the asteroid’s orbit, explained:
“The high-quality observations from optical and radar telescopes have enabled us to rule out any future impacts between the Earth and 2012 TC4. These observations also help us understand subtle effects such as solar radiation pressure that can gently nudge the orbit of small asteroids.”
Multiple observatories also dedicated their optical telescopes to studying how fast TC4 rotates. As Eileen Ryan – the director of the Magdalena Ridge Observatory, which conducted observations of the asteroids rotation – indicated, “The rotational campaign was a true international effort. We had astronomers from several countries working together as one team to study TC4’s tumbling behavior.”
What they found that the small asteroid rotated slowly, which was rather surprising. Whereas small asteroids typically rotate very quickly, TC4 had a rotational period of just 12 minutes, and also appeared to be tumbling. Other observations revealed some interesting things about the shape of TC4.
The Green Bank Telescope, located in West Virginia. Credit: NRAO
These were conducted by astronomers using NASA’s Goldstone Deep Space Network antenna in California, and the National Radio Astronomy Observatory‘s Green Bank Telescope in West Virginia. Their reading helped refine size estimates of the asteroid, indicating that it is elongated and measures approximately 15 meters (50 ft) long and 8 meters (25 feet) wide.
Determining TC4’s composition was more challenging. Due to unfavorable weather conditions that coincided with the flyby, instruments like NASA’s Infrared Telescope Facility (IRTF) at the Mauna Kea Observatory in Hawaii were unable to get a good look at the asteroid. However, spectra was obtained on the asteroid that indicated that it has a rocky body, which means it is an S-type asteroids.
Typically, ground-based elements determine an asteroid’s composition based on their color. Whereas dark asteroids are known for being carbon-rich (C-type), bright asteroids are predominantly composed of silicate minerals (S-type). As Lance Benner, who led the radar observations at JPL, explained:
“Radar has the ability to identify asteroids with surfaces made of highly reflective rocky or metallic materials. We were able to show that radar scattering properties are consistent with a bright rocky surface, similar to a particular class of meteorites that reflect as much as 50 percent of the light falling on them.”
In addition to the observation campaign, NASA used TC4’s latest flyby as an opportunity to test communications between observatories, as well as the internal messaging and communications system that is currently in place. This network connects various government agencies and the executive branch and would come into play in the event of a predicted impact emergency.
Asteroid 2012 TC4 projected flyby of the Earth-Moon system, which was calculated well before it took place. Credits: NASA/JPL-Caltech
According to Vishnu Reddy, an assistant professor from the University of Arizona’s Lunar and Planetary Laboratory who led the observation campaign, this aspect of the exercise “demonstrated that we could organize a large, worldwide observing campaign on a short timeline, and communicate results efficiently.”Michael Kelley, the TC4 exercise lead at NASA Headquarters in Washington, added,”We are much better prepared today to deal with the threat of a potentially hazardous asteroid than we were before the TC4 campaign.”
Last, but not least, was the way the exercise brought scientists and institutions from all around the world together for a single purpose. As Boris Shustov – the science director for the Institute of Astronomy at the Russian Academy of Sciences, who was also part of the exercise – indicated, the exercise was an excellent way to test how the world’s scientific institutions would go about prepping for a possible asteroid impact:
“The 2012 TC4 campaign was a superb opportunity for researchers to demonstrate willingness and readiness to participate in serious international cooperation in addressing the potential hazard to Earth posed by NEOs. I am pleased to see how scientists from different countries effectively and enthusiastically worked together toward a common goal, and that the Russian-Ukrainian observatory in Terskol was able to contribute to the effort. In the future I am confident that such international observing campaigns will become common practice.”
In the event that a Near-Earth asteroid might actually pose a threat the Earth, it is good to know that all the tracking, monitoring and alert systems we have in place are in good working order. If we are going to trust the fate of human civilization (and possibly all life on Earth) to an advanced warning system, it just makes sense to have all the bugs worked out beforehand!
Artist's concept of a large asteroid passing by the Earth-Moon system. Credit: A combination of ESO/NASA images courtesy of Jason Major/Lights in the Dark.
This coming October, an asteroid will fly by Earth. Known as 2012 TC4, this small rock is believed to measure between 10 and 30 meters (30 and 100 feet) in size. As with most asteroids, this one is expected to sail safely past Earth without incident. This will take place on October 12th, when the asteroid will pass us at a closest estimated distance of 6,800 kilometers (4,200 miles) from Earth’s surface.
That’s certainly good news. But beyond the fact that it does not pose a threat to Earth, NASA is also planning on using the occasion to test their new detection and tracking network. As part of their Planetary Defense Coordination Office (PDCO), this network is responsible for detecting and tracking asteroids that periodically pass close to Earth, which are known as Potentially Hazardous Objects (PHOs)
In addition to relying on data provided by NASA’s Near-Earth Object (NEO) Observations Program. the PDCO also coordinates NEO observations conducted by National Science Foundation (NSF)-sponsored ground-based observatories, as well as space situational awareness facilities run by the US Air Force. Aside from finding and tracking PHOs, the PDCO is also responsible for coming up with ways of deflecting and redirecting them.
On Oct. 12, 2017, asteroid 2012 TC4 will safely fly past Earth at an estimated distance of 6,800 km (4,200 mi). Credits: NASA/JPL-Caltech
The PDCO was officially created in response to the NASA Office of Inspector General’s 2014 report, titled “NASA’s Efforts to Identify Near-Earth Objects and Mitigate Hazards.” Citing such events as the Chelyabinsk meteor, and how such events are relatively common, the report indicated that coordination, early warning and mitigation strategies were needed for the future:
“[I]n February 2013 an 18-meter (59 foot) meteor exploded 14.5 miles above the city of Chelyabinsk, Russia, with the force of 30 atomic bombs, blowing out windows, destroying buildings, injuring more than 1,000 people, and raining down fragments along its trajectory… Recent research suggests that Chelyabinsk-type events occur every 30 to 40 years, with a greater likelihood of impact in the ocean than over populated areas, while impacts from objects greater than a mile in diameter are predicted only once every several hundred thousand years.”
The PDCO was established in 2016, which makes this upcoming flyby the first chance they will have to test their network of observatories and scientists dedicated to planetary defense. Michael Kelley is the program scientist and the NASA Headquarters lead for the TC4 observation campaign, which has been monitoring 2012 TC4 for years. As he said in a recent NASA press statement:
“Scientists have always appreciated knowing when an asteroid will make a close approach to and safely pass the Earth because they can make preparations to collect data to characterize and learn as much as possible about it. This time we are adding in another layer of effort, using this asteroid flyby to test the worldwide asteroid detection and tracking network, assessing our capability to work together in response to finding a potential real asteroid threat.”
Diagram showing the data gathered from 1994-2013, indicating daytime (orange) and nighttime (blue) impacts of small meteorites. Credit: NASA
In addition, the flyby will be an opportunity to reacquire 2012 TC4, which astronomers lost track of in 2012 when it moved beyond the range of their telescopes. For this reason, people like Professor Vishnu Reddy of the University of Arizona are also excited. A member of the Lunar and Planetary Laboratory, Reddy also leads the campaign to reacquire the asteroid. As he indicated, this flyby will be a chance for collaborative observation.
“This is a team effort that involves more than a dozen observatories, universities and labs across the globe so we can collectively learn the strengths and limitations of our near-Earth object observation capabilities,” he said. “This effort will exercise the entire system, to include the initial and follow-up observations, precise orbit determination, and international communications.”
2012 TC4 was originally discovered on Oct. 5th, 2012, by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at the Haleakala Observatory in Hawaii. After it sped past Earth in that same year, it has not been directly observed since. And while it is slightly larger than the meteor that exploded in Earth’s atmosphere near Chelyabinsk, Russia, in 2013, scientists are certain that it will pass us by at a safe distance.
This is based on tracking data that was collected by scientists from NASA’s Center for Near-Earth Object Studies (CNEOS). After monitoring 2012 TC4 for a period of seven days after it was discovered in 2012, they determined that at its closest approach, the asteroid will pass no closer than 6,800 km (4,200 mi) to Earth. However, it is more likely that it will pass us at distance of about 270,000 km (170,000 mi).
The Pan-Starrs telescope at dawn. The mountain in the distance is Mauna Kea, about 130 kilometers southeast. Credit: pan-starrs.ifa.hawaii.edu
This would place it at a distance that is about two-thirds the distance between the Earth and the Moon. The last time this asteroid passed Earth, it did so at a distance that was one-quarter the distance between the Earth and the Moon. Therefore, the odds of it passing by without incident are even greater this time around. So rather than representing a threat, the passage of this asteroid represents a good chance for research.
As Paul Chodas, the manager of the CNEOS at NASA’s Jet Propulsion Laboratory, stated:
“This is the perfect target for such an exercise because while we know the orbit of 2012 TC4 well enough to be absolutely certain it will not impact Earth, we haven’t established its exact path just yet. It will be incumbent upon the observatories to get a fix on the asteroid as it approaches, and work together to obtain follow-up observations than make more refined asteroid orbit determinations possible.”
By monitoring 2012 TC4 as it flies by, astronomers will be able to refine their knowledge about the asteroid’s orbit, which will help them to predict and calculate future flybys with even greater precision. This will further mitigate the risk posed by PHOs down the road, and help the PDCO to develop and test strategies to address possible future impacts.
In short, remain calm! This flyby is a good thing!
This illustration depicts the spacecraft of NASA’s Psyche mission orbiting the metal asteroid Psyche (pronounced SY-kee). Solar power with electric propulsion will be used to propel the spacecraft to Psyche. The asteroid’s average distance from the sun is about three times the Earth’s distance or 280 million miles. Credit: SSL/ASU/P. Rubin/NASA/JPL-Caltech
I’m getting psyched for Psyche, which is both the name of an asteroid orbiting the sun between Mars and Jupiter and NASA’s mission to the asteroid. Part of the reason for this excitement comes from learning today that NASA has moved up the launch one year to 2022, with a planned arrival in the asteroid belt in 2026 — four years earlier than the original timeline.
The mission team calculated a new trajectory to Psyche, one eliminating the need for an Earth gravity assist, that would get the probe there about twice as fast and reduce costs.
Fly over Psyche in this cool animation
“We challenged the mission design team to explore if an earlier launch date could provide a more efficient trajectory to the asteroid Psyche, and they came through in a big way,” said Jim Green, director of the Planetary Science Division at NASA Headquarters in Washington. “This will enable us to fulfill our science objectives sooner and at a reduced cost.”
Campo del Cielo meteorites are heavy, metallic and dimpled with regmaglypts or “thumbprints” where softer materials melted away during the meteorite’s fall through the air. This small fragment was once part of a different planetary core similar to Psyche. Credit: Bob King
With a diameter of over 120 miles (200 km), Psyche is one of the ten most massive asteroids in the main asteroid belt. Like certain meteorites found on Earth, it’s made almost entirely of nickel-iron metal. Metal is usually found as pepper-like flecks in stony meteorites, which represent the crust of an asteroid. Heat released during the formation of a large asteroid or planet causes the rock to melt, releasing heavier elements like iron and nickel which trickle downward under the force of gravity to form a metallic core. Radioactivity can also play a role in heating the rock.
A 3-D model of the asteroid Psyche based on its light curve, ie. variations in brightness as it rotates. Credit: Astronomical Institute of the Charles University: Josef ?urech, Vojt?ch Sidorin / CC BY 4.0
That’s why Psyche’s kind of weird. How do you get a 120-mile-wide body of exposed metal floating around space? Astronomers think it was the core of a developing planet — a protoplanet — and probably covered once upon a time by a mantle of rock. Through collisions with other asteroids, that rock layer was eventually blasted away, exposing the metal core. As such, it offers a unique look into the violent collisions that created Earth and the terrestrial planets.
Planets start as small planetesimals (10-100 kilometers across) and grow by gathering up material from new impacts until becoming large enough to serve as embryos for planets. Psyche may have started down the road of planethood only to be chopped down to size by hit-and-run impacts that broke away at its rocky envelope. Credit: Arizona State University
After a 4.6 year cruise that includes a Mars gravity assist flyby, the spacecraft will arrive at Psyche and spend 20 months in orbit mapping and studying the asteroid’s properties. The scientific goals of the mission are to understand the building blocks of planet formation and explore a new type of asteroid never seen up close before. The mission team will seek to find out whether Psyche is the core of an early planet, how old it is, what its surface is like and whether it formed in similar ways to Earth’s core.
Who knows, maybe we’ll learn it was once large enough to be considered a planet just like our own. You can stay in touch with mission developments on their Twitter site.
Asteroid impacts on Mars could have generated supersonic winds that shaped the surface, according to a new study. Credit: geol.umd.edu
The study of another planet’s surface features can provide a window into its deep past. Take Mars for example, a planet whose surface is a mishmash of features that speak volumes. In addition to ancient volcanoes and alluvial fans that are indications of past geological activity and liquid water once flowing on the surface, there are also the many impact craters that dot its surface.
In some cases, these impact craters have strange bright streaks emanating from them, ones which reach much farther than basic ejecta patterns would allow. According to a new research study by a team from Brown University, these features are the result of large impacts that generated massive plumes. These would have interacted with Mars’ atmosphere, they argue, causing supersonic winds that scoured the surface.
These features were noticed years ago by Professor Peter H. Schultz, a professor of geological science with the Department of Earth, Environmental, and Planetary Sciences (DEEPS) at Brown University. When studying images taken at night by the Mars Odyssey orbiter using its THEMIS instrument, he noticed steaks that only appeared when imaged in the infrared wavelength.
Artist’s conception of the Mars Odyssey spacecraft. Credit: NASA/JPL
These streaks were only visible in IR because it was only at this wavelength that contrasts in heat retention on the surface were visible. Essentially, brighter regions at night indicate surfaces that retain more heat during the day and take longer to cool. As Schultz explained in a Brown University press release, this allowed for features to be discerned that would otherwise not be noticed:
“You couldn’t see these things at all in visible wavelength images, but in the nighttime infrared they’re very bright. Brightness in the infrared indicates blocky surfaces, which retain more heat than surfaces covered by powder and debris. That tells us that something came along and scoured those surfaces bare.”
Along with Stephanie N. Quintana, a graduate student from DEEPS, the two began to consider other explanations that went beyond basic ejecta patterns. As they indicate in their study – which recently appeared in the journal Icarus under the title “Impact-generated winds on Mars” – this consisted of combining geological observations, laboratory impact experiments and computer modeling of impact processes.
Ultimately, Schultz and Quintana concluded that crater-forming impacts led to vortex-like storms that reached speeds of up to 800 km/h (500 mph) – in other words, the equivalent of an F8 tornado here on Earth. These storms would have scoured the surface and ultimately led to the observed streak patterns. This conclusion was based in part on work Schultz has done in the past at NASA’s Vertical Gun Range.
An infrared image revealing strange bright streaks extending from Santa Fe crater on Mars. Credit: NASA/JPL-Caltech/Arizona State University.
This high-powered cannon, which can fire projectiles at speeds up to 24,000 km/h (15,000 mph), is used to conduct impact experiments. These experiments have shown that during an impact event, vapor plumes travel outwards from the impact point (just above the surface) at incredible speeds. For the sake of their study, Schultz and Quintana scaled the size of the impacts up, to the point where they corresponded to the impact craters on Mars.
The results indicated that the vapor plume speed would be supersonic, and that its interaction with the Martian atmosphere would generate powerful winds. However, the plume and associated winds would not be responsible for the strange streaks themselves. Since they would be travelling just above the surface, they would not be capable of causing the kind of deep scouring that exists in the streaked areas.
Instead, Schultz and Quintana showed that when the plume struck a raised surface feature – like the ridges of a smaller impact crater – it would create more powerful vortices that would then fall to the surface. It is these, according to their study, that are responsible for the scouring patterns they observed. This conclusion was based on the fact that bright streaks were almost always associated with the downward side of a crater rim.
IR images showing the correlation between the streaks and smaller craters that were in place when the larger crater was formed. Credit: NASA/JPL-Caltech/Arizona State University
As Schultz explained, the study of these streaks could prove useful in helping to establish that rate at which erosion and dust deposition occurs on the Martian surface in certain areas:
“Where these vortices encounter the surface, they sweep away the small particles that sit loose on the surface, exposing the bigger blocky material underneath, and that’s what gives us these streaks. We know these formed at the same time as these large craters, and we can date the age of the craters. So now we have a template for looking at erosion.”
In addition, these streaks could reveal additional information about the state of Mars during the time of impacts. For example, Schultz and Quintana noted that the streaks appear to form around craters that are about 20 km (12.4 mi) in diameter, but not always. Their experiments also revealed that the presence of volatile compounds (such as surface or subsurface water ice) would affect the amount of vapor generated by an impact.
In other words, the presence of streaks around some craters and not others could indicate where and when there was water ice on the Martian surface in the past. It has been known for some time that the disappearance of Mars’ atmosphere over the course of several hundred million years also resulted in the loss of its surface water. By being able to put dates to impact events, we might be able to learn more about Mars’ fateful transformation.
The study of these streaks could also be used to differentiate between the impacts of asteroids and comets on Mars – the latter of which would have had higher concentrations of water ice in them. Once again, detailed studies of Mars’ surface features are allowing scientists to construct a more detailed timeline of its evolution, thus determining how and when it became the cold, dry place we know today!
