We have a new exoplanet announcement this morning – no, it’s not phosphine, or aliens!!! :D It’s the first planet found orbiting a white dwarf host star!

Okay what does that mean and why is it cool (literally and figuratively!).

White dwarfs are remnant cores of stars like the Sun after they’ve used up all their hydrogen and helium. Our Sun will become a white dwarf in ~5 billion years, or what will feel like roughly another two months of 2020.

Time is relative.
The inner planets (Mercury, Venus, and possibly Earth) will be engulfed as the star balloons up to a red giant, rapidly burning through its remaining reserves of fuel. Then it will puff off those outer layers to become a planetary nebulae!
Left behind will be a small, cooling hunk of carbon and oxygen. How small? Very small. Today’s white dwarf, WD 1856+534 , is about 1.3% the size of the Sun. You know what else is about that size? The Earth.

(Graphic of a typical white dwarf from astronomy.ohio-state.edu/~pogge/Ast162/…)
The planets beyond Earth’s orbit will undergo significant dynamical instability as the mass distribution of the whole centre of the solar system is rearranged. Which ones will survive? Which ones will be kicked out? Which ones will be kicked IN?
We have found rocks (planetesimals, mini-planets) and debris orbiting white dwarfs before, hints of previous planetary systems disrupted and destroyed by the spectacular orbital dance of a system flung into gravitational disarray.

In fact, our very first evidence of exoplanets can now be traced back to a white dwarf spectrum from 103 years ago, showing pollution of the star’s surface by heavy elements that could only be there if it had recently eaten some big rocks!

(Ask @newtomato about the rediscovery!)
With @NASA's TESS mission, we found that WD 1856 was being eclipsed by something every 1.4 days. But this was something BIG. The eclipses were huge, >50% deep. That was exciting! Here’s the TESS data from our paper. Preeeetty! Also, v-shaped, so something was just grazing by.
In fact, it was a giant planet!!! (Actually, right on the border between a giant planet and a brown dwarf). Here’s my terrible graphic of their relative sizes. Yes those are powerpoint textures. The planet is ~7 times the size of the star. #notanillustrator
Somehow, this planet survived! Was it like the giant planets of our solar system, forming far out from the star, surviving the red giant expansion, before being chaotically flung inwards? What planetary siblings were lost on the way?
WD 1856 b, as it is now known, is really interesting. For one thing, it’s quite cool (only 165K, despite its proximity to the white dwarf!), and it’s a good target for atmospheric observations (via transmission spectroscopy). That’s a rare combination right now!!!
Also, it gives us tantalizingly more information about what might befall our own solar system, in five billion years. Will Jupiter or Saturn survive the Sun’s big show? Will Earth?! Maybe WD 1856 b will help us find out!
Look, when we designed the new @NASAExoArchive overview pages, we weren't counting on planets that were bigger than their stars. 🤣 (Stars are scaled to fill the graphic height, planets some fraction thereof.)

But now it's Exoplanet Archive-official!


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More from @aussiastronomer

14 Sep
Okay, here's what I told folks who asked about the detection of phosphine (PH3) in the atmosphere of Venus: If you give me the options of unknown chemistry, unknown geology, or unknown biology, then biology is always going to be a distant third behind the other two options.
We see phosphine in other places in the solar system, and it's not biological. Now, terrestrial planets are not the same as gas giants, for sure! But I think we're a ways away from ruling out chemistry and geology as sources of phosphine.
And honestly, with an extraordinary claim like extraterrestrial life, you do have to 100% rule out every other possible origin.

Here's the terribly poorly-kept-secret article!

Read 6 tweets
16 Jun
I had a long chat this morning with a counsellor from the Caltech Staff and Faculty Consultation Center. The last three months have been A LOT, for many of us. I wanted to share what I found helpful. This post is for anyone else new to managing anxiety.
There will be nothing new here for people who have dealt with this before. And I don't know if any of this is helpful long-term yet. But, it was helpful even in the moment to have more information, and to feel like there were possible solutions, so I wanted to share them.
(I specifically enjoyed how the counsellors at Caltech, who must deal with a lot of stressed scientists, were like "Okay, let's break this down. It's SCIENCE. Here's the chemistry. Here's the biology. Here's how you hack them.”)
Read 20 tweets
14 Jan
In case your local astronomer seems agitated, the big dog gravitational wave detector @LIGO just detected an ‘unknown or unanticipated’ burst of gravitational waves somewhere deep in space. 👀
It’s fairly well localized, so you can bet everyone with a telescope has pointed it at that little patch of sky right now.

(@d_a_howell points out that it’s located pretty close to behaving-oddly-of-late superstar Betelgeuse.)
In case you’re wondering, lots of telescopes have ‘Target of Opportunity’ programs. Instead of getting scheduled time, folks can override whoever is on the telescope (YES EVEN IN THE MIDDLE OF A TRANSIT) if something super cool happens, and repoint it wherever they want.
Read 4 tweets
22 Dec 19
Now, all the way through!

On the twelfth day of Christmas, astronomy gave me to me...
Twelve billion miles!

Apollo 11 celebrations!

Read 13 tweets
11 Sep 19
GUYS. Two independent announcements today of the same thing: We have found water vapor in the atmosphere of a planet called K2-18 b!


K2-18 b is not a rocky planet. So that's a bummer. But it IS in the 'habitable' zone of its star, meaning under certain assumptions the temperature is right for liquid water on the surface on the planet.

K2-18 b is massive enough (about 8 times the mass of the Earth) that it has a thick, deep, gaseous atmosphere of hydrogen and helium. Very, very unlike our atmosphere.
Read 10 tweets
1 Feb 19
Let’s do it.
Goals of workshop:
1) What is the current state of the field - what do we already know?
2) What are the funded near-future plans? What might we know soon?
3) What are the potential future advances that could be important?
4) How can NASA help?
Intro by @Astro_Wright - what are technosignatures?

(Autocorrect has no idea what to do with the word ‘technosignatures’ if you get even a single letter wrong.)
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