Jupiter's moon Ganymede, the largest moon in the Solar System, seen orbiting Jupiter, the largest planet in the Solar System. This image was taken by the Cassini spacecraft. Image Credit: NASA/JPL/University of Arizona
Ganymede was shaped by pronounced periods of tectonic activity in the past, according to a new paper. It’s no longer active and its surface is more-or-less frozen in place now. But this discovery opens the door to better planning for future missions to Jupiter’s other frozen moon Europa. Unlike Ganymede, Europa is still tectonically active, and understanding past geological activity on Ganymede helps us understand present-day Europa.
Using information from Gaia's second data release, a team of scientists have made refined estimates of the Milky Way's mass. Credit: ESA/Gaia/DPAC
For almost two centuries, scientists have theorized that life may be distributed throughout the Universe by meteoroids, asteroids, planetoids, and other astronomical objects. This theory, known as Panspermia, is based on the idea that microorganisms and the chemical precursors of life are able to survive being transported from one star system to the next.
Expanding on this theory, a team of researchers from the Harvard Smithsonian Center for Astrophysics (CfA) conducted a study that considered whether panspermia could be possible on a galactic scale. According to the model they created, they determined that the entire Milky Way (and even other galaxies) could be exchanging the components necessary for life.
A view of Ceres in natural colour, pictured by the Dawn spacecraft in May 2015. Credit: NASA/ JPL/Planetary Society/Justin Cowart
In 2007, the Dawn mission launched from Earth and began making its way towards two historic rendezvous in the Main Asteroid Belt. The purpose of this mission was to learn more about the history of the early Solar System by studying the two largest protoplanets in the Main Belt – Ceres and Vesta – which have remained intact since their formation.
In 2015, the Dawn mission arrived in orbit around Ceres and began sending back data that has shed light on the protoplanet’s surface, composition and interior structure. Based on mission data, Pasquale Tricarico – the senior scientist at the Planetary Science Institute (PSI) – has also determined that the Ceres also experienced an indirect polar reorientation in the past, where its pole rolled approximately 36° off-axis.
The Mobile Asteroid Surface Scout (MASCOT) snapped this photo of the asteroid Ryugu during descent. The little hopping robot completed its brief mission and successfully transmitted all of its data back to Hayabusa2. Image: German Aerospace Center (CLR).
Earlier this week asteroid Ryugu had a visitor. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu on October 3rd after it was successfully deployed from the Japanese Hayabusa2 space probe. The little hopping robot’s visit was brief however, and it stopped functioning on Oct. 4th.
"The Goblin", or dwarf planet 2015 TG387 shown in comparison to our Solar System's other planets.
Image: Illustration by Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science.
Astronomers have found a new dwarf planet way out beyond Pluto that never gets closer than 65 AUs to the Sun. It’s nicknamed “The Goblin” which is much more interesting than its science name, 2015 TG387. The Goblin’s orbit is consistent with the much-talked-about but yet-to-be-proven Planet 9.
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
In all this time, the question of ‘Oumuamua’s origin has remained unanswered. Beyond theorizing that it came from the direction of the Lyra Constellation, possibly from the Vega system, there have been no definitive answers. Luckily, an international team led by researchers from the Max Planck Institute for Astronomy (MPIA) have tracked ‘Oumuamua and narrowed down its point of origin to four possible star systems.
Analogue astronauts have tested a ground-penetrating radar named ScanMars at a Mar-like area in Oman. Image: OEWF – Austrian Space Forum
There’s solid evidence for the existence of water on Mars, at least in frozen form at the planet’s poles. And a more recent study confirms the existence of liquid water at the south pole. But visitors to Mars will need to know the exact location of usable water deposits at other Martian locations. A ground-penetrating radar called ScanMars may be up to the task.
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). Originally though to be a comet, follow-up observations conducted by the European Southern Observatory (ESO) and others confirmed that ‘Oumuamua was actually a rocky body that had originated outside of our Solar System.
Since that time, multiple studies have been conducted to learn more about this interstellar visitor, and some missions have even been proposed to go and study it up close. However, the most recent study of ‘Oumuamua, conducted by a team of international scientists, has determined that based on the way it left our Solar System, ‘Oumuamua is likely to be a comet after all.
As noted, when it was first discovered – roughly a month after it made its closest approach to the Sun – scientists believed ‘Oumuamua was an interstellar comet. However, follow-up observations showed no evidence of gaseous emissions or a dusty environment around the body (i.e. a comet tail), thus leading to it being classified as a rocky interstellar asteroid.
This was followed by a team of international researchers conducting a study that showed how ‘Oumuamua was more icy that previously thought. Using the ESO’s Very Large Telescope in Chile and the William Herschel Telescope in La Palma, the team was able to obtain spectra from sunlight reflected off of ‘Oumuamua within 48 hours of the discovery. This revealed vital information about the composition of the object, and pointed towards it being icy rather than rocky.
The presence of an outer-layer of carbon rich material also explained why it did not experience outgassing as it neared the Sun. Following these initial observations, Marco Micheli and his team continued to conduct high-precision measurements of ‘Oumuamua and its position using ground-based facilities and the NASA/ESA Hubble Space Telescope.
By January, Hubble was able to snap some final images before the object became too faint to observe as it sped away from the Sun on its way to leaving the Solar System. To their surprise, they noted that the object was increasing its velocity deviating from the trajectory it would be following if only the gravity of the Sun and the planets were influencing its course.
Oumuamua as it appeared using the William Herschel Telescope on the night of October 29. Queen’s University Belfast/William Herschel Telescope
In short, they discovered that ‘Oumuamua was not slowing down as expected, and as of June 1st, 2018, was traveling at a speed of roughly 114,000 km/h (70,800 mph). The most likely explanation, according to the team, is that ‘Oumuamua is venting material from its surface due to solar heating (aka. outgassing). The release of this material would give ‘Oumuamua the steady push it needed to achieve this velocity.
As Davide Farnocchia, a researcher from NASA’s Jet Propulsion Laboratory and a co-author on the paper, explained in a recent ESA press release:
“We tested many possible alternatives and the most plausible one is that ’Oumuamua must be a comet, and that gasses emanating from its surface were causing the tiny variations in its trajectory.”
Moreover, the release of gas pressure would also explain how ‘Oumuamua is veering off course since outgassing has been known to have the effect of perturbing the comet’s path. Naturally, there are still some mysteries that still need to be solved about this body. For one, the team still has not detected any dusty material or chemical signatures that typically characterize a comet.
As such, the team concluded that ‘Oumuamua must have been releasing only a very small amount of dust, or perhaps was releasing more pure gas without much dust. In either case, ‘Oumuamua is estimated to be a very small object, measuring about 400 meters (1312 ft) long. In the end, the hypothesized outgassing of ‘Oumuamua remains a mystery, much like its origin.
Artist’s impression of the interstellar object, ‘Oumuamua, experiencing outgassing as it leaves our Solar System. Credit: ESA/Hubble, NASA, ESO, M. Kornmesser
In fact, the team originally performed the Hubble observations on ‘Oumuamua in the hopes of determining its exact path, which they would then use to trace the object back to its parent star system. These new results mean this will be more challenging than originally thought. As Olivier Hainaut, a researcher from the European Southern Observatory and a co-author on the study, explained:
“It was extremely surprising that `Oumuamua first appeared as an asteroid, given that we expect interstellar comets should be far more abundant, so we have at least solved that particular puzzle. It is still a tiny and weird object, but our results certainly lean towards it being a comet and not an asteroid after all.”
Detlef Koschny, another co-author on the study, is responsible for Near-Earth Object activities under ESA’s Space Situational Awareness program. As he explained, the study of ‘Oumuamua has provided astronomers with the opportunity to improve asteroid detection methods, which could play a vital role in the study of Near-Earth Asteroids and determining if they post a risk.
“Interstellar visitors like these are scientifically fascinating, but extremely rare,” he said. “Near-Earth objects originating from within our Solar System are much more common and because these could pose an impact risk, we are working to improve our ability to scan the sky every night with telescopes such as our Optical Ground Station that contributed to this fascinating discovery.”
Since ‘Oumuamua’s arrival, scientists have determined that there may be thousands of interstellar asteroids currently in our Solar System, the largest of which would be tens of km in radius. Similarly, another study was conducted that revealed the presence of an interstellar asteroid (2015 BZ509) that – unlike ‘Oumuamua, which was an interloper to out system – was captured by Jupiter’s gravity and has since remained in a stable orbit.
This latest study is also timely given the fact that June 30th is global “Asteroid Day”, an annual event designed to raise awareness about asteroids and what can be done to protect Earth from a possible impact. In honor of this event, the ESA co-hosted a live webcast with the European Southern Observatory to discuss the latest science news and research on asteroids. To watch a replay of the webcast, go to the ESA’s Asteroid Day webpage.
A view of Ceres in natural colour, pictured by the Dawn spacecraft in May 2015. Credit: NASA/ JPL/Planetary Society/Justin Cowart
In March of 2015, NASA’s Dawn mission became the first spacecraft to visit the protoplanet Ceres, the largest body in the Main Asteroid Belt. It was also the first spacecraft to visit a dwarf planet, having arrived a few months before the New Horizons mission made its historic flyby of Pluto. Since that time, Dawn has revealed much about Ceres, which in turn is helping scientists to understand the early history of the Solar System.
Last year, scientists with NASA’s Dawn mission made a startling discovery when they detected complex chains of carbon molecules – organic material essential for life – in patches on the surface of Ceres. And now, thanks to a new study conducted by a team of researchers from Brown University (with the support of NASA), it appears that these patches contain more organic material than previously thought.
The new findings were recently published in the scientific journal Geophysical Research Letters under the title “New Constraints on the Abundance and Composition of Organic Matter on Ceres“. The study was led by Hannah Kaplan, a postdoctoral researcher at Brown University, with the assistance of Ralph E. Milliken and Conel M. O’D. Alexander – an assistant professor at Brown University and a researcher from the Carnegie Institution of Washington, respectively.
A new analysis of Dawn mission data suggests those organics could be more plentiful than originally thought. Credit: NASA/Rendering by Hannah Kaplan
The organic materials in question are known as “aliphatics”, a type of compound where carbon atoms form open chains that are commonly bound with oxygen, nitrogen, sulfur and chlorine. To be fair, the presence of organic material on Ceres does not mean that the body supports life since such molecules can arise from non-biological processes.
Aliphatics have also been detected on other planets in the form of methane (on Mars and especially on Saturn’s largest moon, Titan). Nevertheless, such molecules remains an essential building block for life and their presence at Ceres raises the question of how they got there. As such, scientists are interested in how it and other life-essential elements (like water) has been distributed throughout the Solar System.
Since Ceres is abundant in both organic molecules and water, it raises some intriguing possibilities about the protoplanet. The results of this study and the methods they used could also provide a template for interpreting data for future missions. As Dr. Kaplan – who led the research while completing her PhD at Brown – explained in a recent Brown University press release:
“What this paper shows is that you can get really different results depending upon the type of organic material you use to compare with and interpret the Ceres data. That’s important not only for Ceres, but also for missions that will soon explore asteroids that may also contain organic material.”
Enhanced color-composite image, made with data from the framing camera aboard NASA’s Dawn spacecraft, shows the area around Ernutet crater. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
The original discovery of organics on Ceres took place in 2017 when an international team of scientists analyzed data from the Dawn mission’s Visible and Infrared Mapping Spectrometer (VIRMS). The data provided by this instrument indicated the presence of these hydrocarbons in a 1000 km² region around of the Ernutet crater, which is located in the northern hemisphere of Ceres and measures about 52 km (32 mi) in diameter.
To get an idea of how abundant the organic compounds were, the original research team compared the VIRMS data to spectra obtained in a laboratory from Earth rocks with traces of organic material. From this, they concluded that between 6 and 10% of the spectral signature detected on Ceres could be explained by organic matter.
They also hypothesized that the molecules were endogenous in origin, meaning that they originated from inside the protoplanet. This was consistent with previous surveys that showed signs of hydorthermal activity on Ceres, as well others that have detected ammonia-bearing hydrated minerals, water ice, carbonates, and salts – all of which suggested that Ceres had an interior environment that can support prebiotic chemistry.
But for the sake of their study, Kaplan and her colleagues re-examined the data using a different standard. Instead of relying on Earth rocks for comparison, they decided to examine an extraterrestrial source. In the past, some meteorites – such as carbonaceous chondrites – have been shown to contain organic material that is slightly different than what we are familiar with here on Earth.
Artist’s rendition of the Dawn mission on approach to the protoplanet Ceres. Credit: NASA/JPL
After re-examining the spectral data using this standard, Kaplan and her team determined that the organics found on Ceres were distinct from their terrestrial counterparts. As Kaplan explained:
“What we find is that if we model the Ceres data using extraterrestrial organics, which may be a more appropriate analog than those found on Earth, then we need a lot more organic matter on Ceres to explain the strength of the spectral absorption that we see there. We estimate that as much as 40 to 50 percent of the spectral signal we see on Ceres is explained by organics. That’s a huge difference compared to the six to 10 percent previously reported based on terrestrial organic compounds.”
If the concentrations of organic material are indeed that high, then it raises new questions about where it came from. Whereas the original discovery team claimed it was endogenous in origin, this new study suggests that it was likely delivered by an organic-rich comet or asteroid. On the one hand, the high concentrations on the surface of Ceres are more consistent with a comet impact.
This is due to the fact that comets are known to have significantly higher internal abundances of organics compared with primitive asteroids, similar to the 40% to 50% figure this study suggests for these locations on Ceres. However, much of those organics would have been destroyed due to the heat of the impact, which leaves the question of how they got there something of a mystery.
Dawn spacecraft data show a region around the Ernutet crater where organic concentrations have been discovered (labeled “a” through “f”). The color coding shows the strength of the organics absorption band, with warmer colors indicating the highest concentrations. Credit: NASA/JPL-Caltech/UCLA/ASI/INAF/MPS/DLR/IDA
If they did arise endogenously, then there is the question of how such high concentrations emerged in the northern hemisphere. As Ralph Milliken explained:
“If the organics are made on Ceres, then you likely still need a mechanism to concentrate it in these specific locations or at least to preserve it in these spots. It’s not clear what that mechanism might be. Ceres is clearly a fascinating object, and understanding the story and origin of organics in these spots and elsewhere on Ceres will likely require future missions that can analyze or return samples.”
Given that the Main Asteroid Belt is composed of material left over from the formation of the Solar System, determining where these organics came from is expected to shed light on how organic molecules were distributed throughout the Solar System early in its history. In the meantime, the researchers hope that this study will inform upcoming sample missions to near-Earth asteroids (NEAs), which are also thought to host water-bearing minerals and organic compounds.
These include the Japanese spacecraft Hayabusa2, which is expected to arrive at the asteroid Ryugu in several weeks’ time, and NASA’s OSIRIS-REx mission – which is due to reach the asteroid Bennu in August. Dr. Kaplan is currently a science team member with the OSIRIS-REx mission and hopes that the Dawn study she led will help the OSIRIS-REx‘s mission characterize Bennu’s environment.
“I think the work that went into this study, which included new laboratory measurements of important components of primitive meteorites, can provide a framework of how to better interpret data of asteroids and make links between spacecraft observations and samples in our meteorite collection,” she said. “As a new member to the OSIRIS-REx team, I’m particularly interested in how this might apply to our mission.”
The New Horizons mission is also expected to rendezvous with the Kuiper Belt Object (KBO) 2014 MU69 on January 1st, 2019. Between these and other studies of “ancient objects” in our Solar System – not to mention interstellar asteroids that are being detected for the first time – the history of the Solar System (and the emergence of life itself) is slowly becoming more clear.
Artist's impression of the "Black Hole Ultimate Solar System". Credit: planetplanet.net
Shortly after Einstein published his Theory of General Relativity in 1915, physicists began to speculate about the existence of black holes. These regions of space-time from which nothing (not even light) can escape are what naturally occur at the end of most massive stars’ life cycle. While black holes are generally thought to be voracious eaters, some physicists have wondered if they could also support planetary systems of their own.
Looking to address this question, Dr. Sean Raymond – an American physicist currently at the University of Bourdeaux – created a hypothetical planetary system where a black hole lies at the center. Based on a series of gravitational calculations, he determined that a black hole would be capable of keeping nine individual Suns in a stable orbit around it, which would be able to support 550 planets within a habitable zone.
He named this hypothetical system “The Black Hole Ultimate Solar System“, which consists of a non-spinning black hole that is 1 million times as massive as the Sun. That is roughly one-quarter the mass of Sagittarius A*, the super-massive black hole (SMBH) that resides at the center of the Milky Way Galaxy (which contains 4.31 million Solar Masses).
Detection of an unusually bright X-Ray flare from Sagittarius A*, a supermassive black hole in the center of the Milky Way galaxy. Credit: NASA/CXC/Stanford/I. Zhuravleva et al.
As Raymond indicates, one of the immediate advantages of having this black hole at the center of a system is that it can support a large number of Suns. For the sake of his system, Raymond chose 9, thought he indicates that many more could be sustained thanks to the sheer gravitational influence of the central black hole. As he wrote on his website:
“Given how massive the black hole is, one ring could hold up to 75 Suns! But that would move the habitable zone outward pretty far and I don’t want the system to get too spread out. So I’ll use 9 Suns in the ring, which moves everything out by a factor of 3. Let’s put the ring at 0.5 AU, well outside the innermost stable circular orbit (at about 0.02 AU) but well inside the habitable zone (from about 2.7 to 5.4 AU).”
Another major advantage of having a black hole at the center of a system is that it shrinks what is known as the “Hill radius” (aka. Hill sphere, or Roche sphere). This is essentially the region around a planet where its gravity is dominant over that of the star it orbits, and can therefore attract satellites. According to Raymond, a planet’s Hill radius would be 100 times smaller around a million-sun black hole than around the Sun.
This means that a given region of space could stably fit 100 times more planets if they orbited a black hole instead of the Sun. As he explained:
“Planets can be super close to each other because the black hole’s gravity is so strong! If planets are little toy Hot wheels cars, most planetary systems are laid out like normal highways (side note: I love Hot wheels). Each car stays in its own lane, but the cars are much much smaller than the distance between them. Around a black hole, planetary systems can be shrunk way down to Hot wheels-sized tracks. The Hot wheels cars — our planets — don’t change at all, but they can remain stable while being much closer together. They don’t touch (that would not be stable), they are just closer together.”
This is what allows for many planets to be placed with the system’s habitable zone. Based on the Earth’s Hill radius, Raymond estimates that about six Earth-mass planets could fit into stable orbits within the same zone around our Sun. This is based on the fact that Earth-mass planets could be spaced roughly 0.1 AU from each other and maintain a stable orbit.
Given that the Sun’s habitable zone corresponds roughly to the distances between Venus and Mars – which are 0.3 and 0.5 AU away, respectively – this means there is 0.8 AUs of room to work with. However, around a black hole with 1 million Solar Masses, the closest neighboring planet could be just 1/1000th (0.001) of an AU away and still have a stable orbit.
Doing the math, this means that roughly 550 Earths could fit in the same region orbiting the black hole and its nine Suns. There is one minor drawback to this whole scenario, which is that the black hole would have to remain at its current mass. If it were to become any larger, it would cause the Hill radii of its 550 planets to shrink down further and further.
Once the Hill radius got down to the point where it was the same size as any of the Earth-mass planets, the black hole would begin to tear them apart. But at 1 million Solar masses, the black hole is capable of supporting a massive system of planets comfortably. “With our million-Sun black hole the Earth’s Hill radius (on its current orbit) would already be down to the limit, just a bit more than twice Earth’s actual radius,” he says.
Illustration of tightly-packed orbits of Earth-mass planets in orbit around the Sun (in black) vs. around a supermassive black hole (green). Credit: Sean Raymond
Lastly, Raymond considers the implications that living in such a system would have. For one, a year on any planet within the system’s habitable zone would be much shorter, owing to the fact their orbital periods would be much faster. Basically, a year would last roughly 1.6 days for planets at the inner edge of the habitable zone and 4.6 days for planets at the outer edge of the habitable zone.
In addition, on the surface of any planet in the system, the sky would be a lot more crowded! With so many planets in close orbit together, they would pass very close to one another. That essentially means that from the surface of any individual Earth, people would be able to see nearby Earths as clear as we see the Moon on some days. As Raymond illustrated:
“At closest approach (conjunction) the distance between planets is about twice the Earth-Moon distance. These planets are all Earth-sized, about 4 times larger than the Moon. This means that at conjunction each planet’s closest neighbor appears about twice the size of the full Moon in the sky. And there are two nearest neighbors, the inner and outer one. Plus, the next-nearest neighbors are twice as far away so they are still as big as the full Moon during conjunction. And four more planets that would be at least half the full Moon in size during conjunction.”
He also indicates that conjunctions would occur almost once per orbit, which would mean that every few days, there would be no shortage of giant objects passing across the sky. And of course, there would be the Sun’s themselves. Recall that scene in Star Wars where a young Luke Skywalker is watching two suns set in the desert? Well, it would a little like that, except way more cool!
According to Raymond’s calculations, the nine Suns would complete an orbit around the black hole every three hours. Every twenty minutes, one of these Suns would pass behind the black hole, taking just 49 seconds to do so. At this point, gravitational lensing would occur, where the black hole would focus the Sun’s light toward the planet and distort the apparent shape of the Sun.
To illustrate what this would look like, he provides an animation (shown above) created by @GregroxMun – a planet modeller who develops space graphics for Kerbal and other programs – using Space Engine.
While such a system may never occur in nature, it is interesting to know that such a system would be physically possible. And who knows? Perhaps a sufficiently advanced species, with the ability to tow stars and planets from one system and place them in orbit around a black hole, could fashion this Ultimate Solar System. Something for SETI researchers to be on the lookout for, perhaps?
This hypothetical exercise was the second installment in two-part series by Raymond, titled “Black holes and planets”. In the first installment, “The Black Hole Solar System“, Raymond considered what it would be like if our system orbited around a black hole-Sun binary. As he indicated, the consequences for Earth and the other Solar planets would be interesting, to say the least!
