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Tabby's star is at it again. Could it be aliens this time!? Also, astronomers have discovered a planet with the density of styrofoam!

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Hold on to your telescopes, because Tabby’s star just dimmed again!

Two years ago, astronomers spotted a star almost 1300 light years away called KIC 8462852, nicknamed Tabby’s star after the lead researcher, Tabetha Boyaijan. And it’s been baffling them with its weird drops in brightness ever since.

We see stars dim like this all the time when a planet passes in between them and the Earth, which is actually how we find lots of exoplanets. But Tabby’s star randomly becomes up to 20 percent dimmer, which is way too extreme and unpredictable to be caused by a planet orbiting it. And it seems to be getting dimmer over time.

It seems like there has to be something orbiting the star, but we still don’t have a great explanation for these mysterious data. So astronomers have been waiting to observe more dips in brightness to help develop their hypotheses. And last weekend, it finally happened again!

Multiple astronomers reported that Tabby’s star was dimming, which sent researchers around the world running for their telescopes. This was the first time we were able to see the star dim right from the beginning in real time, and gather data with lots of different kinds of telescopes. So it’s also our best chance yet to try and analyze what kind of material might be passing in front of it.

As of Wednesday when we filmed this, there haven’t been any major announcements. But there are a lot of hypotheses from older data that could be supported or disproved. Like, you might remember the paper that suggested this weirdness could be caused by huge alien megastructures, but there are plenty of natural explanations too, like a bunch of crumbling comets.

One idea published last month in the Monthly Notices of the Royal Astronomical Society suggests that Tabby’s star might be digesting a planet! The researchers proposed that, anywhere from a few hundred to thousands of years ago, a planet collided with the star, and released a burst of energy. That could’ve caused the star to get brighter for a while, so all the progressive dimming is actually just the star returning to normal, and the random dips are from leftover debris.

Another hypothesis, published last December in the Physical Review Letters, suggests that an unknown process inside the star is causing its magnetic poles to randomly flip back and forth, which makes its light fluctuate. Most of these explanations sound reasonable, but we need more data to really solve the mystery of Tabby’s star. The answer could even be something we don’t have evidence for yet!

But it’s still probably not aliens. Sorry! Now, Tabby’s star might be pretty weird, but the universe also has its fair share of strange planets.

There are exoplanets where it rains glass, worlds with hot ice, and now there’s KELT-11b, a recently-discovered gas giant that’s about as dense as Styrofoam. The exoplanet was discovered by an international team of astronomers and citizen scientists as part of the KELT, or Kilodegree Extremely Little Telescope, survey, and their findings were recently published in The Astrophysical Journal. Even though their two robotic telescopes might be little, KELT-11b isn’t exactly the smallest gas giant on the block.

The planet, which is about 320 light years away, is almost 40 percent larger than Jupiter, but it still only has one-fifth of Jupiter’s mass. This means the planet is extra puffy and inflated, like Styrofoam, and it’s actually the third-lowest density planet we’ve accurately measured. That big ball of gas could even sound cute, except for the fact that it’s more than 1400 degrees Celsius on the surface… so, there’s that.

We’re not sure exactly what caused the planet to have such a low density, and we’re hoping to figure that out! But what’s especially helpful about 11b is its unusually large atmosphere, extending almost 2800 kilometers into space. It gets a ton of light from its star, which means it’s a perfect candidate for testing our atmosphere-analyzing skills.

To figure out which elements are floating around in a planet’s atmosphere, astronomers use a process called spectroscopy. Planets reflect and absorb different amounts of different wavelengths of light depending on what they’re made of and what’s in their atmosphere, and we can measure that light to determine their compositions. In the future, we’re hoping to use technology like the James Webb Space Telescope to identify elements in the atmospheres around Earth-like planets using spectroscopy.

But since we’re not quite there yet, we can get some practice on gas giants like KELT-11b with bright stars nearby, which will help us figure out what we’ll need to make better atmosphere-observing instruments in the future. So flickering stars and Styrofoam-density planets are fun for us to talk about, but they’re also really useful for researchers! It’s basically a win-win for everyone.

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