News broke last night about a potentially exciting discovery. Tau Ceti might have a family of planets, one of them quite possibly, in the sweet spot for life.
Tau Ceti is a yellow-gold star, obviously, in the constellation Cetus (the Whale.) It’s also one of our stellar neighbors—clocking in at just under 12 light years distant.
It’s a G-type star, so it’s a lot like our sun, although it is a bit dimmer. It’s sun-like qualities and close proximity to “Sector Zero-Zero-One” have made it a popular choice for SETI searches and science fiction writers. It was one of the stars selected for the first “Ear to the Sky Survey” done in 1960. Sadly, no one heard anything from the golden little dot of light at all.
As Tau Ceti is dimmer than our sun, a terrestrial planet would need to orbit it at about seven-tenths of an astronomical unit, or roughly about the orbit of Venus around Sol.
In 2004, a bright dust belt was detected around the star, which infers a dense Kuiper Belt—the home of comets. This belt is believed to have ten times the amount of debris—junk left over from the star’s formation, than our own star system. Any planets orbiting starward of the belt probably undergo periods of heavy bombardment. They probably have spectacular meteor showers regardless.
Because Tau Ceti is so close and so sun-like it’s been the focus of extensive study, perhaps more so than our next-door neighbors at Alpha Centauri. Using radial velocity, a tried-and-true method for finding planets, teams took 6,000 observations of the star, watching every timey-wimey bleep-bloop and every wibble and every wobble. This method gives you a graph with lots upon lots of noise. Statistical processing (of which I do not have a grasp on at all, so I won’t describe it) can find signals in the noise. The signals for possibly five planets, their orbits, and their possible masses was found.
Three of the potential planets hug the star and are torrid, horrid places. One of the planets orbits Tau Ceti at about where Mars orbits Sol. But the fourth potential planet is right in the sweet spot with an orbit of 168 days.
Right where liquid water could exist. It’s also four times the mass of Earth, so it’s not perhaps human habitable. But it could, if it exists, have its own life. This is speculation.
Now, the planets may not exist at all. They may simply be artifacts of a noisy star. I still want these planets to be real. Don’t you?
However, Tuomi's team warns that disturbances on the star itself, rather than orbiting planets, may be producing the small velocity changes in Tau Ceti. "They're really digging deep into the noise here," says Sara Seager, an astronomer at the Massachusetts Institute of Technology in Cambridge who was not part of the team. "The [astronomical] community is going to find it hard to accept planet discoveries from signals so deeply embedded in noise."It’ll take many years of observation to confirm or deny their existence.
"They're pushing the envelope," says Gregory Laughlin, an astronomer at the University of California, Santa Cruz. "Some or even many of these planets could go away. But I think that they've done absolutely the best job that you can do, given the data." Laughlin says it's frustrating that the most interesting planets—small ones like Earth—are so challenging to detect: "You have to get tons and tons and tons of velocity measurements over many years, and then you really, really have to take extreme care—as this Tuomi et al. paper does—to get rid of all the systematic noise."
Team member Chris Tinney, an astronomer at the University of New South Wales in Sydney, Australia, acknowledges the problem. "It's certainly very tantalizing evidence for potentially a very exciting planetary system," Tinney says, but he adds that verifying the discovery may take 10 years, and the scientists didn't want to wait that long. "We felt that the best thing to do was to put the result out there and see if somebody can either independently confirm it or shoot it down."
Oh, and no, Tau Ceti is not the home star of the Vulcan race. That's 40 Eridani.
You can read the actual preprint here (it's a PDF).