‘Pitch black world’: Astronomers observe a really dark exoplanet

Artist’s conception of WASP-12b in orbit around its star. Image Credit: NASA/ESA/G. Bacon (STScI)

Exoplanets, planets orbiting other stars, are now being discovered by the thousands, and in a wide variety of sizes, colours, and compositions. Now, new studies of one of these worlds show that it reflects almost no light, making it appear nearly pitch black.

The new observations of exoplanet WASP-12b were made in October 2016 by an international team of astronomers using the Space Telescope Imaging Spectrograph (STIS) on the NASA/ESA Hubble Space Telescope. They were measuring how much light the planet reflects to learn more about its atmosphere.

“The measured albedo of WASP-12b is 0.064 at most. This is an extremely low value, making the planet darker than fresh asphalt!” said lead author Taylor Bell, a Master’s student in astronomy at McGill University. “The low albedo shows we still have a lot to learn about WASP-12b and other similar exoplanets.”

By comparison, our own Moon is about two times more reflective, with an albedo of 0.12.

WASP-12b is a “hot Jupiter,” orbiting very close to its Sun-like star WASP-12A (its year is just over one Earth day in length), which is 1,400 light-years away. The surface temperature on the daylight side of the planet is about 2,600 degrees Celsius. The planet is also somewhat egg-shaped, due to the strong gravitational pull of the star. Its radius is almost twice that of Jupiter. It was discovered in 2008 and has already been well-studied. The new observations will now help astronomers learn even more about its origin and evolution.

So why is WASP-12b so dark? The extremely high temperature is at least part of the answer, according to astronomers. As Bell explained:

“There are other hot Jupiters that have been found to be remarkably black, but they are much cooler than WASP-12b. For those planets, it is suggested that things like clouds and alkali metals are the reason for the absorption of light, but those don’t work for WASP-12b because it is so incredibly hot.”

The atmosphere is so hot it behaves more like the atmosphere of a low-mass star than a planet, creating a low albedo.

“After we measured the albedo we compared it to spectral models of previously suggested atmospheric models of WASP-12b,” said Nikolay Nikolov of the University of Exeter, UK and co-author of the new study. “We found that the data match neither of the two currently proposed models.”

According to current analysis, the atmosphere of WASP-12b is composed of atomic hydrogen and helium, and it is too hot for clouds to form, and hydrogen molecules are broken down into atomic hydrogen.

Measuring the albedo of exoplanets isn’t easy, and this is only the second exoplanet where it has been done so far. The other is HD 189733b, another hot Jupiter. In that case, the results suggested that the planet had a deep blue colour. For WASP-12b, astronomers had to observe the planet during an eclipse, when it was behind its star for a short time. That way, the amount of light being reflected can be measured directly, as opposed to other methods.

As Bell noted, “The fact that the first two exoplanets with measured spectral albedo exhibit significant differences demonstrates the importance of these types of spectral observations and highlights the great diversity among hot Jupiters.”

Hot Jupiters are fairly common among exoplanets, even though there are none in our own Solar System. The study of WASP-12b will help astronomers better understand other similar giant planets although their compositions may be quite different. Such searingly hot worlds are not too habitable for life, but they are still very interesting of course in their own right, and such planetary systems often have smaller, rocky planets similar in size to Earth. Comparing these systems to our own Solar System will provide more clues as to how it originated and developed to have some planets and moons potentially habitable (and indeed known to be inhabited, of course, in the case of Earth).

This article was first published on Futurism.






Kepler Space Telescope discovers first evidence for exocomets transiting their stars

Artist’s conception of a “storm” of comets orbiting a nearby star. Image Credit: NASA/JPL-Caltech

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.”

Kepler SAP photometry covering 3 days around each of the three larger comet transits. Image Credit: Rappaport et al.
Kepler SAP photometry covering 3 days around each of the three smaller comet transits. Image Credit: Rappaport et al.

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:

The mystery surrounding KIC 8462852 (‘Boyajian’s Star’) has been theorized by some to also involve comets, but the new exocomet paper suggests there may be no connection. Image Credit: NASA

“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.







First exomoon found? Astronomers optimistic but urge caution

Artist’s conception of a large Earth-like exomoon orbiting a giant gaseous exoplanet. Image Credit: Avatar/20th Century Fox

Exoplanets are being found so frequently now that they have become commonplace. But what about exomoons? As might be expected, they are much harder to detect, being typically much smaller than most planets. There have been tantalizing hints but nothing conclusive so far. That may be about to change soon, however. Astronomers from Columbia University have reported the possible discovery of the first exomoon – but they stress that it is still unconfirmed and just a candidate at this point.

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James Webb Space Telescope arrives at Johnson Space Center for cryogenic testing

The giant 18-piece mirror of the James Webb Space Telescope, inside the cleanroom at Johnson Space Center. Photo Credit: NASA/Chris Gunn

Often referred to as the successor for Hubble, the James Webb Space Telescope (JWST) is one of the most highly anticipated space telescopes ever built. A large infrared telescope with a 6.5-metre primary mirror, JWST will be able to look at every phase of the Universe, from the period just after the Big Bang to the formation of stars, galaxies, exoplanets and even our own Solar System. Scheduled for launch in fall 2018, JWST recently arrived at NASA’s Johnson Space Center in Houston, Texas, where it will undergo its last, and crucial, cryogenic test.

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Nearby ‘super-Earth’ exoplanet may be best place yet to search for alien life

Artist’s conception of the exoplanet LHS 1140b. Image Credit: ESO

Just recently, an exo-planetary system called TRAPPIST-1, with seven known planets close in size to Earth, was announced by astronomers. Some of those planets are in the star’s habitable zone, meaning that they could potentially be habitable for some kind of life. Then, another Earth-sized world was found orbiting the star GJ 1132b, and may have water and methane in its atmosphere. Now, another similar planet has been found orbiting another nearby star. It is also close in size to Earth and resides in the star’s habitable zone. According to scientists, it is another prime candidate in the search for alien life and may even be the best one yet.

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