Blogs / Bad Astronomy

Astronomers have just announced that they have found a near twin of Jupiter orbiting the star HD 154345, a fairly sunlike star about 60 light years away. This is very cool news, and has some pretty big implications for finding another Earth around some distant star.

Artist’s impression of an extrasolar planet. Courtesy NASA.

Finding a planet like this isn’t as easy as it sounds! Finding planets with the same mass as Jupiter isn’t hard; many have been found with even lower mass. The hard part is finding one that is orbiting a sun-like star at the same distance Jupiter orbits our Sun. The closer in a planet is to its star, the easier it is to find: the method used measures how hard the planet’s gravity tugs on its parent star as it orbits; the planet pulls the star around just like the star pulls the planet, and we see this as a change in the velocity of the star toward and away from us (called the radial velocity; Wikipedia has a nice animated GIF for this), and that effect gets bigger with bigger planets, and the closer they orbit.

So we see lots of superjupiters orbiting close in, and some lighter planets also close to their parent stars. But finding a Jupiter-like planet on an orbit like Jupiter’s, well, that takes a long time to do. Jupiter takes 12 years to orbit the Sun, so it would take many observations over many years to detect a planet like that.

But they’ve done it! The team (Jason Wright, Geoff Marcy, Paul Butler, and Steven Vogt) have been using the monster 10-meter Keck telescope for ten years, observing HD 154345. This star is a lot like the Sun (it’s a G8, and the Sun is a G0 G2, meaning it’s a little smaller, lower mass, and cooler than the Sun). The planet (called HD 154345b) has a mass of no less than 0.95 times that of Jupiter, and orbits the star 4.2 AU out — 1 AU is the Earth-Sun distance, and Jupiter’s orbit is about 5.2 AU from the Sun. The planet takes a little over 9 years to orbit the star, and the orbit is circular.

As the planet orbits the star, the star’s velocity relative to us changes very slightly in a periodic fashion. In the case of HD 154345, the change in velocity over the course of several years is just 30 meters per second… about the speed of a car on a highway!

This makes HD 154345b the first true Jupiter analog discovered. It’s a tremendous achievement!

So why is this important?

The superjupiters in tight orbits that have been discovered probably didn’t form that close to their stars; it’s a tough environment to form a big planet. The commonly accepted theory is that a planet like that forms farther out from the star and migrates closer in over millions of years, probably due to friction from the disk of gas and dust from which it formed.

Now imagine: you’re a planet that’s about the size of Earth, orbiting your star at about the same distance Earth is from the Sun. You’re pretty happy, thinking that in a few hundred million years, things’ll cool off, you’ll form oceans, and continents, and life. But then, hey, what’s that? Oh, it’s a planet with 500 times your mass, headed right for you! When it passes you by, its tremendous gravity either drops you into the star, or ejects you right out of the system!

Bummer.

So we don’t think that the stars that have close-in massive planets will have Earth-like planets. It may be that the only solar systems with planets like Earth will have their Jupiter analogs orbiting farther out, where they can’t hurt the smaller planets.

And hey, that’s just what we have here!

So, does HD 154345 have a blue-green ball orbiting it as well? These observations can’t say; they are only sensitive enough to find the Jupiter-like planet (and they can’t rule out planets farther out either). It might, or it might not. But here’s an interesting point: the system is probably about 2 billion years old. By that age, the Earth was already teeming with microscopic life. Provocative, eh?

I expect that future missions will spend quite a bit of time peering at this system. As of right now, it holds a lot of promise for those of us hoping that one day we’ll find another Earth.

That cool triple-asteroid I wrote about yesterday? BAUT reader RickJ posted a very cool image he took of it:

He took a series of 30 second exposures with about a one minute gap between them. During each exposure, the asteroid(s) moved a bit across the sky, so it leaves a dotted trail in the picture. Remember, folks, that just because you read of some fancy-schmancy observatory seeing some object, it doesn’t mean you can’t see it yourself with a ’scope of your own!

This is very cool, and I encourage you to peruse the images on BAUT, and post some yourself if you have any!

Scientists working to see if Mars ever had life have concentrated, of course, on looking for water. It appears to have been abundant on Mars a long time ago, but what was it like?

On Earth, water can be pure, or salty, or laden with minerals and metals. On Mars, the presence of minerals like jarosite indicate that at least in some spots, Martian water was high in minerals, with a corresponding high acidity. That’s bad enough, but now evidence from the rover Opportunity indicates that the water was also very salty, far higher in salinity than Earth’s oceans.

This has dimmed somewhat the idea of life on Mars, at least lately — meaning, the last few billion years. It’s possible that the water was in better shape to develop life as we know it early on in the history of Mars, but over time, the water got more acidic and more salty. At first blush, this precludes life arising and flourishing on the Red Planet, but I wonder. One scientist said "This tightens the noose on the possibility of life," but I think that’s a hasty conclusion.

Life arose on Earth almost immediately after the asteroid and comet bombardment ceased, just a billion or so years after Earth formed. Conditions then were very different than they are now, and yet here we are. Whatever life started back then, it evolved, adapted. Every corner of the Earth has life in it, from miles down under the surface to pools of chemicals that would kill a human (and most bacteria) instantly. Check out D. radiodurans for a real eye-opener on how tough life can be. I have little doubt our oceans have changed their salinity numerous times over the past 3 billion years, and life adapted.

From this press release, it’s impossible to say how much things have changed on Mars — besides, of course, the loss of its atmosphere, its water, and the drop in temperature. In this case, I mean how the water on Mars changed over time, and how rapidly. If it happened overnight, then sure, it’s not hard to imagine it wiping out all life on the planet. But what if it took, say, a few million years? Life on Earth has survived horrific circumstances in the past. Could any possible Martian life have done the same?

We still have no idea if life ever arose on Mars or not — Mars cooled more rapidly than the Earth did, and so may have had life on it before we did. If any life did form there, it may not be around anymore, and there could be any number of causes. We simply don’t know, and I think it’s way too early in our exploration of the planet to rule anything out.

Shaquille O’Neal is becoming an astrophysicist? I guess Colbert was on to something.

Money quote:

“I have been involved in many hotly contested battles in my playing career and have come out an even stronger warrior, but 100 billion Kelvins is a lot even for the Diesel,” O’Neal said, showing the various media present a slide of the Crab Nebula, which he called a “frightening” example of what could be left of him after a supernova occurs. “If I were still in my 20s, maybe I could sustain a burst of energy more powerful than the sun could emit over a 10-billion-year time period. But Steve Nash has to understand that I have a bad hip.”

Though I must take exception to this line (emphasis added):

“Not even electron degeneracy pressure is enough to stop a supernova when that happens to a Sun,” O’Neal added. “I don’t even know what that means, and I am the Big Astronomer. But it scares me.”

He’s skirting dangerously close to stepping on my trademark, and I may have to throw an elbow.

But now it looks like I have a new candidate to blurb my book.

Tip o’ the sweatband to Professor Astronomy.

The newest, and heftiest yet, Carnival of Space is being hosted by New Frontiers.

I’ve noticed that when I post about the new Carnival, it doesn’t seem like too many people comment; it’s historically the category of my posts that gets the fewest comments. I’m curious: is that because few people actually care about the Carnival, or it’s not a comment-worthy kind of post, or that you make any comments on the relevant host’s blog?

The CoS is actually a great event; it collects all the best space and astronomy posts of the week and puts them in one place for your reading pleasure. I’ve found several astronomy blogs on the CoS that I now read regularly, so there are tons of reasons to check in. Go read it!

For the record, I think SETI is a good idea, and that most people misunderstand Drake’s equation (it’s a way of estimating the number of civilizations in the galaxy, not a way of determining their number), but still, this XKCD cartoon is funny (click to see the punch line):

Hold the mouse over the picture on the XKCD page to see what he really thinks. I disagree with him on that, too. We’ve only just started looking.

The Delta II rocket that will loft GLAST into space in May has arrived at Cape Canaveral.

How’d you like to see that pass you on the highway? Anyway, I’m posting this a gentle reminder to keep suggesting names for GLAST. As you can see, things are rolling along for launch. Get naming!