Wednesday was an exciting day for space exploration enthusiasts, as NASA announced the two finalist missions selected as part of its New Frontiers Program – a new robotic mission to be launched in the mid-2020s. The two winners are a sample return mission from a comet and a drone-like rotorcraft to further explore Saturn’s moon Titan. Other mission proposals which didn’t make the cut included a sample return mission from the Moon’s south pole, a new Venus lander, a Saturn atmospheric probe and a new Enceladus mission. However, two of those missions, for Enceladus and Venus, were selected for further technology development.
Comets, those icy and rocky bodies with the spectacular long tails of gas and dust, are common in our Solar System, with several thousand having been discovered so far. But what about other solar systems? Thousands of exoplanets are now being discovered, along with the first hints of exomoons, so it seems natural that comets should also exist in at least some of these alien solar systems. Now, NASA’s Kepler Space Telescope has indeed found the first good evidence for comets transiting their host stars.
The transits, thought to be caused by small comet-like bodies, were discovered for two stars in the Kepler data – KIC 3542116 and KIC 11084727. Evidence for comets orbiting other stars has been found before, but this is the first time they have apparently been seen transiting in front of their host stars, just like planets. From the new paper:
“In this work we reported the discovery of six apparent transits in KIC 3542116 that have the appearance of a trailing dust tail crossing the disk of the host star. We have tentatively postulated that these are due to between 2 and 6 distinct comet-like bodies in the system. We also found a single similarly shaped transit in KIC 11084727. Both of these host stars are of F2V spectral types.”
The findings of similar transits for at least two Kepler stars indicates that they may not be rare, that comets, just like planets, may be quite common in other solar systems. The three deepest transits found are all very small, with less than 0.1% of the stars’ light blocked during a transit. All of the transits were found during visual searches of the data, as opposed to computer searches, which strengthens the case that many more such occurrences are waiting to be discovered.
The authors of the new paper also make an interesting comparison to the star KIC 8462852 (aka ‘Boyajian’s Star’) which has attracted a lot of interest from astronomers lately for its weird and still-unexplained dips in brightness which don’t resemble any kind of transits or similar phenomena ever seen before. Some early theories suggested massive “comets” as one possible explanation, but the new paper seems to suggest that is unlikely:
“Finally, the deep dips in the flux of KIC 8462852 (aka ‘Boyajian’s Star’; Boyajian et al. 2016) are worth trying to relate to what is observed in KIC 3542116. By contrast, the largest flux dips in the former star reach 22% which is more than two orders of magnitude greater than the transits we see in KIC 3542116. Furthermore, the dips in KIC 8462852 can last for between 5 and 50 days, depending on how the beginning and end points of the dip are defined. These are one to two orders of magnitude longer than for the transits in KIC 3542116. Finally, we note that none of the dips in KIC 8462852 has a particularly comet-shaped profile. There have been a number of speculations about the origin of the dips in KIC 8462852, including material resulting from collisions of large bodies and moving in quasi-regular orbits (Boyajian et al. 2016); swarms of very large comets (Boyajian et al. 2016); and even a ring of dusty debris in the outer Solar System (Katz 2017). However, there is currently no compelling evidence for any of these scenarios.”
This article was first published on AmericaSpace.
Jupiter has been in the news a lot lately, with the Juno spacecraft continuing to send back stunning new images of the largest planet in the Solar System, including close-ups of the Great Red Spot. But something else happened at this time 23 years ago which captured astronomers’ and the public’s attention – a huge explosion in Jupiter’s atmosphere as a comet broke apart and the fragments collided with the planet, plummeting into the deep, thick atmosphere. The impacts and resulting “scars” were observed by telescopes around the world.
The search for evidence of extraterrestrial intelligence is one of the most exciting pursuits in astronomy today. Needless to say, there is a lot of controversy and debate surrounding the topic, partly due to an event which happened in 1977 – the famous “Wow!” signal. The brief but unusual radio transmission was detected only once, and the debate over its origin has continued to this day. Now, a group of astronomers are claiming to have finally solved the mystery. According to their new study just published, the signal came not from aliens, but comets.
As has been reported previously, there is something weird going on around a star which is a little over 1,400 light-years away. Astronomers are still baffled as to just what that is, and theories have ranged from a huge mass of comets to alien megastructures. Indeed, comets had become the leading explanation offered for the star’s odd behaviour, although that was really just the best of a bunch of ideas which all had flaws in them. Now, new research shows that the comet explanation is even less likely to be the answer, although the actual explanation is still as elusive as ever. Needless to say, this has resulted in a lot of discussion and debate in the past few months.