A New Potentially Habitable Planet from TESS

Illustration of the orbits of the planets in the TOI-700 system. Credit: NASA.

This week is what many call the “Super Bowl of Astronomy”: the winter meeting of the American Astronomical Society (AAS), held this year in Honolulu. I am not there, sadly, but I am involved in one of the big press stories to come out of there.

Extrasolar planets are one of the many fields of astronomy that are announcing discoveries at the AAS, and one of the biggest stories is that NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first “potentially habitable”* planet, TOI-700 d. As it happens, I am one of the coauthors (along with 92 others) on the first of the three papers about this planet that were announced yesterday, which is not something you get to say often about a paper with its own press conference, even at NASA.

This paper is about the discovery of TOI-700’s three planets and a little bit about what we can infer about their atmospheres. For the record, the second paper was about using the Spitzer Space Telescope to observe the planets, both to prove that they’re really there (a fraction of these “detections” are actually binary stars in the background) and to potentially measure some actual data about the atmosphere. (As an aside, Spitzer is being retired on January 30, so this was a really last-minute thing.) And the third paper wasn’t about observing the planet directly, but about making theoretical models for the atmosphere to figure out what it will take to measure the composition of the atmosphere.

TESS is tasked with scanning the half million brightest stars in the sky for transiting planets. These are planets that pass directly in front of their stars. They’re are only a small fraction of all the planets out there, but they are the easiest to study, and by looking at the brightest stars, TESS finds planets that are closer and even easier to study than the ones found by Kepler.

TOI-700 is a red dwarf star—type M2 with a brightness only 2.3% that of our Sun. This is important because TESS mostly looks only at short-period planets, and you need a small, cool star for short-period planets to be cool enough to be habitable. TOI-700 has three planets: b, c, and d, but it’s planet d that everyone is talking about. Planet d orbits its star in 37 days; its size is such that it should have a solid surface, and (if it has a similar atmosphere) its temperature should be very close Earth’s.

Unfortunately, it will be 5-10 years before we can get good enough observations to tell what’s in the atmosphere of this planet. What I think is more interesting is the middle planet, planet c. Planet c orbits in 16 days. At that distance, we would expect it to be a lot like Venus, but it’s not. It’s a mini-Neptune with a radius 2.7 times as large as Earth, which almost certainly means it has a deep hydrogen atmosphere.

This is very interesting because to find a planet with this kind of hydrogen atmosphere in between two planets that don’t have one is unusual. Planets in the same solar system are usually about the same size, like Venus and Earth, and it’s uncommon to see such a large difference in planets that are right next to each other.

I caution that this part is not in the paper, and I didn’t do a detailed analysis because it wasn’t the subject of the paper, but TOI-700 c is close to the boundary where you would expect to see a deep hydrogen atmosphere evaporated away by the starlight. It will take more observations to tell, but there may be something unusual about its atmosphere. Getting good observations of TOI-700 c will be much easier, and it think they could give us valuable information about how planetary atmospheres form and evolve.

One very important measurement is to find the masses of all three planets. This is much easier to do with radial velocities and can probably be done within the year. Once we know the exact masses of the planets, we will be able to estimate the properties of their atmospheres much better. TOI-700 is ongoing proof that it is a very exciting time in the field of exoplanets.

I do want to take some time to explain the name of the star because it confused even me, and I work in this field.

TOI-700 means “TESS Object of Interest #700.” For Kepler, candidate planets were calls KOIs, while confirmed planets got their own Kepler numbers, like Kepler-22. (Like I mentioned, a lot of them were false alarms.) But there’s not much point in doing this for TESS because all of the stars TESS is watching have their own catalog numbers. Most of these are at least semi-memorable, like Pi Mensae or GJ 357. However, we use TOI-700 for this one because its proper catalog number is 2MASS J06282325-6534456. 2MASS stands for the Two-Micron All Sky Survey, the most important infrared survey of the sky, done from 1997-2001. And that long string of numbers are the coordinates of the star in the sky. Usually, they shorten it to something like 2M0628 for quick reference, such as if you’re writing a paper about many 2MASS objects, but TOI-700 is easier to remember and work with.

* To many of us astronomers, “potentially habitable” isn’t very good terminology. It implies more than it really means. What it means is only that the planet has a solid surface and is a temperature where it could have liquid water, but there’s no proof that it does have liquid water, let alone life. I might write more on this later.

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How to Make New Year’s Resolutions that Work


Okay, I can’t really justify writing a headline like that. My new year’s resolutions for 2019 only sort of worked…But considering most new year’s resolutions fail by mid-February, I guess I’m doing better than most. So what’s my secret? It’s simple.

I make new year’s resolutions every three months.

No, I’m serious. I changed my new year’s resolutions every three months to improve them. I changed them so much that it’s hard to describe exactly how will I did, but here is a quick summary.

Exercising: completion rate 31%.
Reading: completion rate 94%.
Writing: completion rate 84%.
Blog posts: completion rate 83%.
Publishing attempts: completion rate 48%.

That is indeed better than most people do, and changing them as I went definitely helped. So how did I do it? Well, I’m not exactly sure how I arrived at my ideas, but from experience, I have a few pieces of advice that I think will apply generally.

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What’s coming in Astronomy in the 2020s

At this time of year, many news sites, blogs, and others like to post a year in review…I’m not going to do that. It’s been a long, crazy year, much like the four-ish years before that. The news cycle has just gone so crazy that I don’t feel like spending the time to put one together.

Instead, since it’s not just the end of the year, but the end of the 2010s, I thought I would look ahead at what exciting new astronomy and astrophysics stories we’re likely to see in the 2020s. I could talk about science in general for this. Will we eradicate polio? Start cloning humans? Use CRISPR for gene therapy? But I’m not so well versed in those things, so I think I’ll play it safe and stick to astronomy.

New Telescopes

James Webb Space Telescope rendering

Possibly the biggest story in astronomy over the next decade will be the James Webb Space Telescope (JWST). This replacement for the Hubble Space Telescope will launch on March 31, 2021* and will tell us more about planets, the early universe, and everything in between than ever before.

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Two New Bible Reading Plans

A Gutenberg Bible. Probably not the most practical version for reading. Credit: Mark Pellegrini.

This is just a quick follow-up to my post from five years ago when I read the Bible in one year and posted my customized reading plan, and from earlier this year when I re-posted it as an essay.

Long story short, I didn’t like the formatting on that essay, so I decided to redo it (with a few corrections). In the process, I decided to also write a second reading plan, covering the Bible in chronological order. (Maybe I’ll read the chronological plan for 2020.) Click here to see the new essay, containing both plans and a brief explanation.

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A Challenge to Flat Earthers


Is the Earth round? Most people say yes, obviously. But a growing (or at least growing in loudness) number on the internet say no. Flat Earthers are (or seem to be) real, and they seem to have an answer to every argument that we are living on a spinning globe.

But shouldn’t it be obvious that the Earth is round, you ask? How do you explain the sunrise and sunset or time zones if Earth is flat? What about ships disappearing over the horizon? But Flat Earthers will say it’s refraction*—light bending through the atmosphere makes things appear to vanish over the horizon. What about the circular shadow of the Earth during a lunar eclipse? Most of them say Earth is a circular disk, so it can still cast a circular shadow (even though there are lots of other problems like that).

Fine, but there are quantitative experiments that can be done to measure the curvature of the Earth, aren’t there? Eratosthenes’ shadows and so forth. Surveying equipment over the ocean or flat stretches of water. Taking a photo from a high-altitude balloon or actual space. But no. Conspiracies, conceptual errors, and camera artifacts, they say. These things are all difficult for the average layperson to measure, and it’s hard to account for all the complications when you do. (Camera distortions are very real, especially over wide angles.)

However, I thought of an idea. It wasn’t even about proving Earth is round at first; I was just wondering if I could see the curvature of the Earth. But I realized it applies here, and it’s something that I haven’t seen in my admittedly limited reading on the subject.

So here is my Flat Earth Challenge. This is an experiment that you personally can do with nothing but a smartphone, a ruler, and a window seat on a commercial airliner: Take a photo of the horizon from the plane and measure the curvature. I tried to do this myself during my trip to Iceland a few months ago, but I wasn’t able to get a window seat during daylight, so I couldn’t get a good shot. I’ll try it again the next time I fly. (If there are any fellow astrophysicists reading who are going to the AAS, try it on your flight to Hawaii.)

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Movie Review: Star Wars: The Rise of Skywalker


Well, here it is: the end* of the Star Wars saga. Episode IX: The Rise of Skywalker is the completion of the nine-film series George Lucas originally promised us in 1978. It took 41 years, selling the series to Disney, a lot of noise over The Last Jedi, and some false starts of spin-offs to do it…but they finally did it.

Sadly, The Rise of Skywalker hasn’t received the hype that The Force Awakens did in 2015. Reality has ensued in the intervening years, and Disney has not been able to put up the consistent quality and build-up of interest that it did with Avengers: Endgame earlier this year. However, this is still one of the biggest events for one of the most beloved science fiction franchises of all time.

And…I wasn’t impressed. My rating is 3 out of 5.

No spoilers here, or not much you couldn’t guess from the trailer. Frankly, this movie felt more like Star Wars fanfiction than actual Star Wars. Without getting into details, it was rushed and choppy almost the whole way through, up until the final battle. There were gratuitous cameos that didn’t really add anything to the plot. There were feats of technology that ignored the established lore. There were new Force powers that were way beyond anything we’ve seen before to the point of breaking my suspension of disbelief. And an awful lot of time was spent trying to fix the mistakes (or “mistakes”) of The Last Jedi (a few of which caused more problems).

Then, on top of all that, it was a classic case of trying to do too much, and in this case, it wasn’t really needed. This wasn’t based on an especially long book or something. It was all, “we have to go to this place and then this other place to find this person and then do this other thing” when several of those could have been cut out to simplify the plot. (And all in an alarmingly short space of in-story time.) I don’t have the time or space here to break it down scene by scene and compare it with the other films, but I think they were trying to do a lot more than the others—easily two movies’ worth.

Okay, there were a couple things I did really like. There were little references to the past mistakes of the franchise as a whole (not just The Last Jedi) like the First Order learning from the “single point of failure” mistakes of the past. The final battle in general was pretty good. And most especially, one theme I really liked in The Last Jedi, the theme of empowering the people, paid off really well in The Rise of Skywalker, although it still could have been explored in a lot more depth.

Star Wars really is an impressive achievement. It had two exceptionally good movies back in the 1970s, and those two movies have carried the franchise to being the second-highest grossing film series of all time (behind only the Marvel Cinematic Universe). True, it had one other truly excellent film, The Force Awakens, but it was kind of a rip-off of the original. Return of the Jedi was only pretty good. Attack of the Clones is arguably underrated (except for “I don’t like sand.”) And personally, I loved The Last Jedi, but it was really a love it or hate it kind of film. Unfortunately, The Rise of Skywalker doesn’t improve that score.

I’ve argued before that the best thing for Star Wars as a franchise would be to strip everything back to the original trilogy and film the best of the novels, starting from Timothy Zahn’s Heir to the Empire trilogy. In other words, create a “Star Wars Cinematic Universe” building on what is now Star Wars Legends (formerly the Expanded Universe).

After seeing The Rise of Skywalker, I still wish Disney would do that, if they do anything. They have the formula. They have proven and time-tested material to use. And they could do a lot better than what they’ve done with the sequel trilogy.

But for now, that’s all she wrote. May the Force be with you.

*Until the Mouse says otherwise.

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Cosmology in the 1980s: The Dark Matter Flowchart

Last week, I wrote about Jim Peebles of Princeton receiving the Nobel Prize in Physics for his body of work in cosmology. However, there’s another cosmology-related essay I’ve been wanting to write for a long time.

The Dark Matter Flowchart is a humorous flowchart (think like an XKCD comic) created by three Princeton grad students and one researcher circa 1986. It described the state of the field of cosmology at the time in hilarious fashion, and a depressingly large amount of it is still relevant today.

I first saw the Flowchart on the wall of the grad student lounge at Princeton, and I’ve been wanting to update it or at least annotate it ever since. I finally took the time to draw up a more legible version and explain all of the references contained within.

Special thanks to Dr. David Weinberg and Dr. Barbara Ryden for answering my questions about the Flowchart. My new version is below, and you can read my essay annotating it here.

Click to enlarge.
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