In August 2014, the ESA’s Rosetta spacecraft arrived at its destination, Comet 67P/Churyumov-Gerasimenko, after a 10 year journey. Rosetta carried a small companion, the Philae Lander. On November 12th, Philae was sent to the surface of Comet 67P. Unfortunately, things didn’t go exactly as planned, and the lander’s mission lasted only 63 hours.
During that time, it gathered what data it could. But mission scientists weren’t certain of its precise location, meaning its data was difficult to interpret accurately. Only when scientists knew precisely where Philae was located on the comet, could they make best use of all of its data.
In 2017, astronomers and the world were surprised to learn that an interstellar object (named ‘Oumuamua) passed by Earth on its way to the outer Solar System. After multiple surveys were conducted, scientists were left scratching their heads as to what this object was – which speculation ranging from it being a comet or an asteroid to comet fragment or even an extra-terrestrial solar sail!
But one of the greatest takeaways from that event was the discovery that such objects pass through our Solar System on a regular basis (and some stay). And as it turns out, astronomers with NASA, the ESA, and the International Scientific Optical Network (ISON) announced the detection of what could be a second interstellar object! Could this be ‘Oumuamua 2.0? And if so, what mysteries might it present?
Since it was first detected hurling through our Solar System, the interstellar object known as ‘Oumuamua has been a source of immense scientific interest. Aside from being extrasolar in origin, the fact that it has managed to defy classification time and again has led to some pretty interesting theories. While some have suggested that it is a comet or an asteroid, there has even been the suggestion that it might be an interstellar spacecraft.
However, a recent study may offer a synthesis to all the conflicting data and finally reveal the true nature of ‘Oumuamua. The study comes from famed astronomer Dr. Zdenek Sekanina of the NASA Jet Propulsion Laboratory, who suggests that ‘Oumuamua is the remnant of an interstellar comet that shattered before making its closest pass to the Sun (perihelion), leaving behind a cigar-shaped rocky fragment.
On October 31st, 2015, NASA tracked a strange-looking comet as it made a close flyby of Earth. This asteroid, known as 2015 TB145, was monitored by the multiple observatories and radar installation of the agency’s Deep Space Network. Because of the timing and the skull-like appearance of this asteroid, scientists nicknamed it the “Death Comet”.
Naturally, there was no reason to worry, as the asteroid posed no threat and passed within about 498,900 km (310,000 mi) of Earth. But the timing and the appearance of the comet were nothing if not chilling. And coincidentally enough, the “Death Comet” (aka. “The Great Pumpkin Comet”), will be passing Earth for the second time, this time shortly after Halloween.
The mission recently started science operations (on July 25th, 2018) and is expected to transmit its first collection of data back to Earth this month. But before that, the planet-hunting telescope took a series of images that featured a recently-discovered comet known as C/2018 N1. These images helped demonstrate the satellite’s ability to collect images over a broad region of the sky – which will be critical when it comes to finding exoplanets.
As the name would suggest, the TESS mission is designed to search for planets around distant stars using the Transit Method (aka. Transit Photometry). For this method, distant stars are monitored for periodic dips in brightness, which are indications that a planet is passing in front of the star (aka. transiting) relative to the observer. From these dips, astronomers are able to estimate a planet’s size and orbital period.
This method remains the most effective and popular means for finding exoplanets, accounting for 2,951 of the 3,774 confirmed discoveries made to date. To test its instruments before it began science operations, TESS took images of C/2018 N1 over a short period near the end of the mission’s commissioning phase – which occurred over the course of 17 hours on July 25th.
The comet that it managed to capture, C/2018 N1, was discovered by NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) satellite on June 29th. This comet is located about 48 million km (29 million mi) from Earth in the southern constellation Piscis Austrinus. In these pictures, which were compiled into a video (shown below), the comet is seen as a bright dot against a background of stars and other objects.
As it moves across the frame (from right to left), the comet’s tail can be seen extending to the top of the frame, and gradually changes direction as the comet glides across the field of view. The images also reveal a considerable amount of astronomical activity in the background. For instance, image processing causes the stars to shift between white and black, which highlights some variable stars visible in the images.
These are stars that change brightness as a result of pulsation, rapid rotation, or being eclipsed by a binary neighbor. A number of Solar System asteroids are also visible as small white dots moving across the field of view. Last, but not least, some stray light that was reflected from Mars is also visible near the end of the video. This light appears as a faint broad arc that moves across the middle section of the frame, from left to right.
This effect was due to the fact that Mars was at its brightest at the time since it was near opposition (i.e. at the closest point in its orbit to Earth). These images showcase the capabilities of the TESS mission, even though they only show a fraction of the instrument’s active field of view.
In the coming weeks and months, TESS science team will continue to fine-tune the spacecraft’s performance as it searches for extra-solar planets. As noted, it is expected that TESS will find thousands of planets in our galaxy, vastly increasing our knowledge of exoplanets and the kinds of worlds that exist beyond our Solar System!
And be sure to check out the video of the images TESS captured, courtesy of NASA’s Goddard Space Flight Center:
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.
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.
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.
The European Space Agency’s Rosetta mission was an ambitious one. As the first-ever space probe to rendezvous with and then orbit a comet, Rosetta and its lander (Philae) revealed a great deal about the comet 67p/Churyumov-Gerasimenko. In addition to the learning things about the comet’s shape, composition and tail, the mission also captured some incredible images of the comet’s surface before it ended.
For instance, Rosetta took a series of images on June 1st, 2016, that showed what looks like a blizzard on the comet’s surface. Using these raw images (which were posted on March 22nd, 2018), twitter user landru79 created an eye-popping video that shows just what it would be like to stand on the comet’s surface. As you can see, its like standing in a blizzard on Earth, though scientists have indicated that it’s a little more complicated than that.
The video, which consists of 25 minutes worth of images taken by Rosetta’s Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), was posted by landru79 on April 23rd, 2018. It shows the surface of 67p/Churyumov-Gerasimenko on the loop, which lends it the appearance of panning across the surface in the middle of a snowstorm.
However, according to the ESA, the effect is likely caused by three separate phenomena. For instance, the snow-like particles seen in the video are theorized to be a combination of dust from the comet itself as well as high-energy particles striking the camera. Because of OSIRIS’ charge-coupled device (CCD) – a radiation-sensing camera – even invisible particles appear like bright streaks when passing in front of it.
As for the white specks in the background, those are stars belonging to the Canis Major constellation (according to ESA senior advisor Mark McCaughrean). Since originally posting the video, landru79 has posted another GIF on Twitter (see below) that freezes the starfield in place. This makes it clearer that the comet is moving, but the stars are remaining still (at least, relative to the camera’s point of view).
And of course, the entire video has been sped up considerably for dramatic effect. According to a follow-up tweet posted by landru79, the first image was shot on June 1st, 2016 at 3.981 seconds past 17:00 (UTC) while the last one was shot at 170.17 seconds past 17:25.
Si apilamos todo el set alineando con las estrellas de fondo se distingue mejor que son estrellas y q es polvo (olvidaos de rayos cósmicos ) #ROSETTA ? OSIRIS #67P/CHURYUMOV-GERASIMENKO new albums ?–ROSETTA EXTENSION 2 MTP030– Miércoles 1 Junio 2016 all filters stacked? pic.twitter.com/UyZ628JxKP
Still, one cannot deny that it is both captivating and draws attention to what Rosetta the mission accomplished. The mission launched in 2004 and reached 67P/Churyumov-Gerasimenko in 2014. After two years of gathering data, it was deliberately crashed on its surface in 2016. And yet, years later, what it revealed is still captivating people all over the world.
Astronomers this week announced that they had discovered an asteroid or comet on a trajectory that brought it from outside the Solar System? Is this the first case of an object from deep space? And what can we learn from this discovery?
The latest discovery was made by a team of international astronomers led by the Max Planck Institute for Solar System Research. Using Hubble, they spotted a unique object in the Main Asteroid Belt – a binary asteroid known as 288P – which also behaves like a comet. According to the team’s study, this binary asteroid experiences sublimation as it nears the Sun, which causes comet-like tails to form.
Using the Hubble telescope, the team first observed 288P in September 2016, when it was making its closest approach to Earth. The images they took revealed that this object was not a single asteroid, but two asteroids of similar size and mass that orbit each other at a distance of about 100 km. Beyond that, the team also noted some ongoing activity in the binary system that was unexpected.
As Jessica Agarwal explained in a Hubble press statement, this makes 288P the first known binary asteroid that is also classified as a main-belt comet. “We detected strong indications of the sublimation of water ice due to the increased solar heating – similar to how the tail of a comet is created,” she said. In addition to being a pleasant surprise, these findings are also highly significant when it comes to the study of the Solar System.
Since only a few objects of this type are known, 288P is an extremely important target for future asteroid studies. The various features of 288P also make it unique among the few known wide asteroid binaries in the Solar System. Basically, other binary asteroids that have been observed orbited closer together, were different in size and mass, had less eccentric orbits, and did not form comet-like tails.
The observed activity of 288P also revealed a great deal about the binary asteroids past. From their observations, the team concluded that 288P has existed as a binary system for the past 5000 years and must have accumulated ice since the earliest periods of the Solar System. As Agarwal explained:
“Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few meters thick… The most probable formation scenario of 288P is a breakup due to fast rotation. After that, the two fragments may have been moved further apart by sublimation torques.”
Naturally, there are many unresolved questions about 288P, most of which stem from its unique behavior. Given that it is so different from other binary asteroids, scientists are forced to wonder if it merely coincidental that it presents such unique properties. And given that it was found largely by chance, it is unlikely that any other binaries that have similar properties will be found anytime soon.
“We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question,” said Agarwal. In the meantime, this unique binary asteroid is sure to provide astronomers with many interesting opportunities to study the origin and evolution of asteroids orbiting between Mars and Jupiter.
In particular, the study of those asteroids that show comet-like activity (aka. main-belt comets) is crucial to our understanding of how the Solar System formed and evolved. According to contrasting theories of its formation, the Asteroid Belt is either populated by planetesimals that failed to become a planet, or began empty and gradually filled with planetesimals over time.
In either case, studying its current population can tell us much about how the planets formed billions of years ago, and how water was distributed throughout the Solar System afterwards. This, in turn, is crucial to determining how and where life began to emerge on Earth, and perhaps elsewhere!
Be sure to check out this animation of the 288P binary asteroid too, courtesy of the ESA and Hubble: