Paid subscribers expand my world

As of this writing, astronomers have discovered nearly 6,300 exoplanets: alien worlds orbiting alien stars. The first was discovered in the early 1990s. When a new, dedicated mission launches into space the total number found tends to jump up, like when Kepler went into operation, as well as TESS (the Transiting Exoplanet Survey Satellite).

Sometimes there’s a much smaller jump in discoveries when someone digs through the data and finds more exoplanets. At those times we see a dozen more, sometimes a couple of dozen. 

And then there’s the T16 Project. They just published the results of their new technique to look for planets, and where they found 10,061 new planet candidates. 

WHAT.

Yup. They found 11,554 candidate exoplanets in total, but about 1,000 were previously found and another 411 don’t have enough data to be conclusive, leaving the 10,091 new ones. [link to journal paper].

Again, up until now 6,300 have been found. If confirmed, this passel will way more than double the known exoplanets.

The “if confirmed” part is important. Astronomers are a bit conservative when it comes to claims like this, and want to be sure they pass a bunch of tests to make sure everything was done correctly and these planets actually exist. Having said that, the process the astronomers went through looks legit to me, and I would bet the majority of these new candidates are real.

That’s amazing.

TESS works by scanning the sky over and over again, carefully measuring the brightness of every star it sees many times during each scan. If a star has a planet, and we happen to see that orbit edge on, then once per orbit the planet passes directly in front of the star, creating a mini-eclipse called a transit, and the star dims. By plotting the brightness over time — what we call the star’s light curve — we can see a distinctive pattern to the dip in light which can be used to determine a lot about the planet, including its distance from the star and the planet’s size. 

The best way to do this is to see many transits, because if we see the planet orbit around the star several times it gives us a better handle on the planet’s period (its year), and also confirms that the planet exists at all. 411 of the candidates (not included in the 10,091) are single transit events, putting them on shakier ground, but it’s still entirely possible they’re real.

This project looked at data from the first year of TESS observations. They got light curves for a staggering 54 million stars, all brighter than about 16^th magnitude (about one-ten thousandth as bright as the faintest star you can see by eye).

What they did then was detrend those light curves. Some stars are naturally variable, getting brighter and dimmer over time. Sometimes there are instrumental effects that affect the light curves, and so on. The astronomers applied various mathematical fits to the curves, then used that to “flatten” the curves and get rid of those trends. This makes any small transit dip far easier to spot.

They used a form of neural net to analyze the data, basically an algorithm that can be “trained” to look for features in the light curves, and be able to tell real effects from false positives. That’s how they winnowed down the number to just over 10,000 planets.

By the nature of the observations, they tend to find big planets close-in to their host stars, because these make bigger dips and do so with shorter periods (so the transits are seen more often). The majority of the planets they found have periods of 3-4 days. Yes, days. We call these planets hot Jupiters for a reason; they are extremely close to their host stars (which is why their periods are so short) and get cooked by them. These orbits are typically perhaps 10 million kilometers in radius; for comparison Mercury — the closest planet to the sun, with a surface temperature hot enough to melt lead — is about 50 million. So yeah, these planets are broiling.

There may be longer-period planets in the data too (like those 411 single-transit ones they found) but these are harder to confirm, and by the nature of the geometry are more rare the farther out the planet is. In fact, while the transit method of finding exoplanets works very well, it misses the vast majority of planets because their orbits aren’t edge-on. We can look at the geometry of orbits, though, and extrapolate up to how many should exist from what we do see, and that’s how we find that, on average, every star in the galaxy has one planet. In reality, though, some don’t have any, while some, like the sun, have many.

But either way, there are hundreds of billions, perhaps trillions, of planets in our Milky Way galaxy alone.

Mind you, this new result is based on only about 15% of the TESS data, too (it’s been observing for over eight years now). The first year didn’t cover the whole sky, and as more observations are processed fainter stars will be seen, too. So as they continue this work to cover the entire current observations set they expect to find even more planets.

This is the power of a General Observer mission, where the data are archived and made public, so that scientists from around the world can get them and figure out new ways to analyze them. Before T16 published their results there were 885 confirmed planets found using TESS, and just shy of 8,000 candidates. That latter number just went way up.

The implications of this are phenomenal. We already had decent statistics on the number of stars with planets, and are getting good stats for the kinds of planets seen, too — hot Jupiters, super-Earths, mini-Neptunes, and more. But the more we find the better those statistics get, and the more we understand about how stars make planets. And while there are many scientific goals for these studies, one that resonates with us as humans is the search for other Earths: planets the right size and distance from their host stars to possibly have conditions similar to our own home world. Those are hard to find; Earths are small and the longer period makes them difficult to spot.

But, given the statistics, they’re out there. And we’ll find them.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!