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SYFY WIRE Bad Astronomy

First light for TESS!

By Phil Plait
A chunk of sky near Beta Centauri (the bright star near the bottom) seen by the TESS spacecraft in its very first image. Credit: NASA / MIT / TESS

NASA's newest planet-finding machine, the Transiting Exoplanet Survey satellite — TESS — launched into space on April 18, 2018. Since that time it's been on what's best described as a Rube Goldberg orbit. It's used its onboard rocket several times to increase the size of its elliptical orbit around Earth, and then, on May 17, it got close enough to the Moon (about 8,000 km) to use its gravity to radically alter the spacecraft's trajectory, changing not just the shape but the tilt of the orbit. One more burn on May 30 and it'll be in the correct orbit to start up its science.

It'll sweep the sky over and over again, using its relatively small cameras to take images of huge swaths of sky, measuring the brightnesses of hundreds of thousands of stars. Periodic dips in the starlight will reveal the presence of exoplanets, alien worlds orbiting alien stars.

It's a monumental task, and I can show you just how big it is, because NASA just released the "first light" image from TESS, a test photo taken to make sure everything is functioning well onboard:

A chunk of sky near Beta Centauri (the bright star near the bottom) seen by the TESS spacecraft in its very first image. Credit: NASA / MIT / TESS

Whoa. This image shows a couple of hundred thousand stars (I assume; that's what NASA has claimed, and I decided not to count them all), and they showed up in a mere two-second exposure! Mind you, this is one small patch of sky about 10° on a side, and TESS will be looking at the entire sky over a period of two years. That's 40,000 square degrees, 400 times bigger than this image.

When I first saw this image I could tell right away it was in or very near the plane of the Milky Way. Our galaxy is a flat disk, and we're in that disk, so the plane appears as a fuzzy streak of light stretching across the sky. When magnified, that fuzz resolves itself into millions of stars, so when you look into the plane of the galaxy you're seeing far more stars than when you look up and away from it. There's also long streaming filaments of dark dust in the galactic plane, and you can see those in the image, too.

But where is this, exactly? When the image was first released on Twitter, it didn't say. So I fired up Sky Safari and scanned around the Milky Way, but couldn't place it. I was about ready to give up when my pal Alex Parker tweeted he had it:

By using an online astrometry program, the field was identified as being near Beta Centauri (also called Hadar) in the southern sky. The NASA press release (which I saw later) also says that the edge of the wondrous Coal Sack dark nebula can be seen to the upper right as well (I was later able to determine that the bright glow in the upper part is called Cederblad 122).

I immediately zoomed in on that part of the sky using my own software and laughed out loud. Ah, that explains why I couldn't find it: The image from TESS is reversed left-to-right! Amazing how much harder that can make IDing it.

Mind you, this is not the final way TESS images will look! Again, this is a preliminary engineering test shot, and over time the cameras will be adjusted to produce the best possible images. The first science first light image should happen in June.

And then the fun begins. Unlike the Kepler observatory, which stared at one spot in space, focusing on 150,000 or so stars that were relatively faint, TESS will look at brighter stars. The reasoning behind this is that while Kepler was looking to find as many planets as possible, TESS is looking for ones that are closer (and therefore easier to study for follow-up), given that brighter stars tend to be closer to Earth.

So think of this as our first "howdy, neighbor!" photo from an observatory that's going to find lots and lots of our neighborhood planets. Thousands of them, in fact. It'll likely double the number of confirmed exoplanets known and will be a bounty for planetary scientists.

Remember: 30 years ago we didn't know of a single planet outside our solar system. Now we know of several thousand. 30 years hence, who knows? It's a big galaxy. And we're just getting started.