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New Search for Alien Life with Deep-Space Observatory

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More Alien Worlds! NASA to Announce

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Scientists Have Discovered a 'Puffy' Exoplanet With The Density of Styrofoam

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Astronomers have found a giant exoplanet larger than Jupiter, but with extremely low mass - a composition that gives this mysterious 'puffy planet' a density very similar to styrofoam.

The team who found KELT-11b, which orbits a star located about 320 light-years from Earth, says this "extraordinarily inflated" world is the third-lowest density planet with a precisely measured mass and radius that has been discovered – and this oddball, lightweight sphere could tell us more about how such strange exoplanets evolve.

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"It is highly inflated, so that while it's only a fifth as massive as Jupiter, it is nearly 40 percent larger, making it about as dense as styrofoam, with an extraordinarily large atmosphere," says astronomer Joshua Pepper from Lehigh University in Pennsylvania.

Apart from KELT-11b's unusual density, one of the things that makes the exoplanet stand out is its host star's extreme brightness. The star, called KELT-11, is in the process of evolving into a red giant, meaning it's started using up its nuclear fuel, fusing hydrogen in a shell outside its core.

Scientists now predict that sometime within the next 100 million years, KELT-11b will end up being engulfed by its host star, as KELT-11's outer layers expand to consume the styrofoam-like world.

That engulfment won't take long, either, since the planet hangs very close to its host, orbiting KELT-11 in less than five days. But before that engulfment happens, the puffy planet stands to teach scientists more about its atmospheric makeup, thanks to the intense brightness generated by KELT-11.

The star is in fact the brightest visible star in the Southern Hemisphere that's known to host a transiting planet – referring to how KELT-11b passes in between the star and Earth during its orbit.

That transit is how astronomers often detect exoplanets, as the amount of light space telescopes receive from these distant stars dips slightly as the exoplanet passes in front of them. But in the case of KELT-11, the sub-giant's intense luminosity meant that the dip in light caused by KELT-11b's transit was barely recognisable to astronomers using the KELT (Kilodegree Extremely Little Telescope) survey – a pair of robotic telescopes located in Arizona and South Africa.

"This discovery was very challenging. The original KELT observations of the star – its light curve – showed only a hint of the transit. Because the transit is both shallow (a little under 0.3 percent change in brightness) and long, it was very difficult to obtain reliable, complete confirmation observations." Pepper told Tomasz Nowakowski at Phys.org last year, when the team first announced their findings prior to peer-review.

Follow-up observations eventually confirmed the existence of KELT-11b, and now the same extreme backlight that made its initial discovery so difficult could help the team figure out the composition of its atmosphere. And that could provide clues on how this styrofoam world got so unusually inflated.

As it stands, KELT-11b is about twice as large as the scientists can explain, given its mass and proximity to its host, but now that we know it's there, it's a great opportunity to find out more about these styrofoam-like planets, and what makes them so big but so sparse at the same time.

"We think that KELT-11b will be a great test case to help us understand the mechanism that causes inflated planets. Furthermore, since the host star has evolved onto the sub-giant branch and is reaching the end of its life, we hope that we can study the behaviour of planetary systems at the end-stage of their star's lifetime." Pepper told Phys.org.

The findings are reported in The Astronomical Journal.

A Strange, Primitive Atmosphere Has Been Discovered Around a Water-Rich Alien World

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Unexpected findings about the atmosphere of a distant Neptune-sized world have surprised scientists, acting as a reminder that as we discover more about planets beyond our Sun, the lessons we've learned from our own Solar System certainly don't always apply.

In this case, HAT-P-26b – located some 437 light-years away from Earth – is what's called a 'warm' or 'hot Neptune', meaning its mass is similar to Neptune, but that the planet closely orbits its host star. These kinds of worlds have been discovered before, but nothing quite like HAT-P-26b.

"Astronomers have just begun to investigate the atmospheres of these distant Neptune-mass planets, and almost right away, we found an example that goes against the trend in our Solar System. This kind of unexpected result is why I really love exploring the atmospheres of alien planets." says one of the researchers, Hannah Wakeford from NASA's Goddard Space Flight Centre.

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What's unusual about HAT-P-26b is its unexpectedly primordial atmosphere, composed almost entirely of hydrogen and helium. For a planet that hangs so close to its star – orbiting it in just 4.23 days, in fact – that breaks a pattern astronomers are used to seeing in the atmospheric composition of other planets.

As it happens, that tight orbit is what made HAT-P-26b easy to study. One of the ways scientists can research the atmosphere of alien worlds is by observing planets as they transit (pass in front of) their host stars. When planets do this, telescopes can analyse the starlight that gets filtered by the planet's atmosphere, which can tell us about the chemicals that make up that airspace.

Using data from NASA's Hubble and Spitzer space telescopes, Wakeford's team found that HAT-P-26b's atmosphere is largely clear of clouds but reveals a strong water signature – what the researchers say is the best measurement to date of water on an exoplanet of this size. Crucially, that water signature enabled the team to estimate HAT-P-26b's metallicity: the extent to which the planet's atmosphere is dominated by elements heavier than hydrogen and helium.

In the case of our own Solar System, metallicities are lower for bigger planets – evidenced by the gas giants Jupiter and Saturn, with Jupiter having a metallicity up to 5 times that of the Sun, while Saturn contains about 10 times as much as the Sun.

What this means is that their atmospheres are mostly made up of hydrogen and helium. By contrast, Uranus and Neptune, which are smaller and orbit the Sun more distantly, contain greater metallicity – of around 100 times that of the Sun.

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The pattern here is that, among our Solar System's outer planets at least, metallicities are lower for the bigger planets that lie closer to the Sun. Scientists think that this is because, when these worlds formed from the protoplanetary dust that surrounded the Sun when the Solar System was young, Jupiter and Saturn were bombarded by less icy debris rich in heavy elements.

As a result, their subsequent atmospheres retain less metallicity today. But in the case of HAT-P-26b, we've got a world that's not far out from its host star – and is in fact virtually clinging to it – and yet its atmosphere is almost entirely composed of hydrogen and helium, much like Jupiter and Saturn.

"[T]hat means that it probably formed much closer to its star, or later in the disc lifetime where it wasn't bombarded by icy debris and rich heavy elements whilst it was forming. We did not know that you could form these-sized planets closer to their star." Wakeford told Amina Khan at the Los Angeles Times, although in either case the researchers say it's a surprising result.

While it's definitely a quirk, it's an incredibly valuable one for astronomers, because it tells us that there are a lot more planetary possibilities than the template laid down in our own cosmic neighbourhood – and that means there's more surprising space science coming our way in the future.

"This analysis shows that there is a lot more diversity in the atmospheres of these exoplanets than we were expecting, which is providing insight into how planets can form and evolve differently than in our Solar System. I would say that has been a theme in the studies of exoplanets: Researchers keep finding surprising diversity." one of the team, David K. Sing from the University of Exeter in the UK, explains in a press release.

The findings are reported in Science.