New Extrasolar Planet Photos to Shake Up Astronomy

The scoop: Astronomers have directly imaged four extrasolar planets for the first time -- and without the skepticism of former claims. Exoplanet expert Sara Seager explains what the findings mean for humanity.

Dave on Earth (1:38 PM): Hi Sara -- Dave Mosher of Discovery Space here.

Exoplanet Sara (1:41 PM): Hi Dave, I'm here!

Dave on Earth (1:42 PM): Excellent.
Let's jump right in: What do you do for a living, and where?

Exoplanet Sara (1:44 PM): I'm a professor of planetary science and physics at MIT, near Boston.
Right now, however, I'm at the airport waiting to fly to California. Leaves in about one hour.

Dave on Earth (1:44 PM): That's a nice real-world constraint on our chat, then.
Where are you headed?

Exoplanet Sara (1:46 PM): To a team meeting for NASA's Kepler Space Telescope, which is planned for launch in March 2009. Kepler will answer the question, "How common are other Earths?"
So we're very excited. (Sorry -- had to plug that in here somewhere!)

Dave on Earth (1:47 PM): No problem :)
Any ideas about how common planets like Earth are?

Exoplanet Sara (1:48 PM): No solid ideas right now. Right now we can only find big, massive planets like Jupiter (300 times the Earth's mass).
We can extrapolate though... we know that every single star is born with a disk of material around it, and so planets should form.
Just what kind of planets form depends.

Dave on Earth (1:51 PM): Blind guessing isn't very scientific, but what would you say the odds of Earth-like planets are in stars with a disk of stuff?
Then I'll pester you about some brand-new exoplanet findings.

Exoplanet Sara (1:52 PM): I'm an optimist. I'd guess more than half of all stars have planets similar to Earth!

Dave on Earth (1:52 PM): Score one for aliens!

Exoplanet Sara (1:53 PM): Whether or not those planets have aliens is another story :)

Dave on Earth (1:53 PM): Of course.
So before we jump into the new exoplanet stuff, what would you say exoplanet hunting has been going lately?

Exoplanet Sara (1:55 PM): It's been crazy lately. Lots of amazing discoveries. Lots of wild ideas to work out.

Dave on Earth (1:57 PM): Feel like you can hardly keep up? If so, I'm with you.

Exoplanet Sara (1:58 PM): That's a good way to put it :)

Dave on Earth (1:58 PM): Ok, these two new studies: What did astronomers find?

Exoplanet Sara (1:59 PM): Astronomers have taken direct pictures of exoplanets.
This is very hard -- like finding a needle in a haystack.

Dave on Earth (2:01 PM): The last time I checked, there was only one exoplanet photographed.
Even then people were skeptical (possibly a failed star).

Exoplanet Sara (2:02 PM): Yes indeed, several claims of directly imaged exoplanets have been made in the past.
The problem is that most people would not call them planets. We have a bit of an identity crisis over how to define the word "planet".

Dave on Earth (2:03 PM): So there are four new planets images -- three around a star a bit bigger than our sun, and another around Fomalhaut.
Are you saying we're not certain they're planets?

Exoplanet Sara (2:06 PM): Most people will agree these new "planets" are bona fide planets, although the debate will continue.
I think the new discoveries will force us to redefine the word "planet".
The debate is still raging about Pluto. Pluto is no longer officially a planet, but many scientists think it should be.
Now we're looking at the big planet end, instead of the small planet end.

Dave on Earth (2:08 PM): I see... so we're burning the scientific candle at both ends.
What is planet-like about the four new ones imaged?

Exoplanet Sara (2:10 PM): As you mentioned, star HR 8799 has three planets orbiting it. So, the motion of the planets around the star has been seen.
We've never seen three stars all orbiting another star -- only planets do this.
The problem is that most astronomers want to call something a planet only if its mass is less than 13 Jupiter masses.
With direct imaging, however, we can't measure the planets' masses. We have to infer the mass from other measurements -- and two of the three planets may be above that mass limit.

Dave on Earth (2:13 PM): If scientists want to keep them out of the planet club, what do they propose we call them, then?

Exoplanet Sara (2:14 PM): Brown dwarfs (aka failed stars).
Planets aren't supposed to generate their own energy. Brown dwarfs generate a teensy bit when they're young.
The planet around Fomalhaut is more likely to be within the mass limit, and it has sculpted a dust ring. The shape and edge of the dust ring has allowed astronomers to infer the planet's mass.

Dave on Earth (2:15 PM): The dust ring around the star?

Exoplanet Sara (2:16 PM): Yes, it encircles whole star and is extremely huge.

Dave on Earth (2:16 PM): Sounds like these discoveries will shake some things up a bit (more).
You've been studying exoplanets for awhile; how important would you say these findings are? Findings = the exoplanets, of course.

Exoplanet Sara (2:18 PM): This is a case where 1 + 1 is greater than 2!
In other words, these discoveries legitimize the technique of direct detection.
That method is also a tantalizing taste of the future -- we want to take such images of planets much closer to the star, like the Earth.

Dave on Earth (2:20 PM): So the race is on to find more planets this way. Thanks!

Exoplanet Sara (2:20 PM): Hey -- I'm about to board my plane, in five minutes.
I feel like we are not finished... Should we pick this up later?

Dave on Earth (2:21 PM): Sounds like a great idea.

Exoplanet Sara (2:22 PM): Tomorrow morning work for you?
I could squeeze something in later today, during the meeting (but don't publish that!)

Dave on Earth (2:22 PM): I don't want to get you in trouble, so let's chat tomorrow :)

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Dave on Earth (8:31 AM): Good morning!

Exoplanet Sara (8:32 AM): Hello! Every day my job is to be as quantitative as possible when talking and writing, so this is a nice break.

Dave on Earth (8:32 AM): Glad to help.
Ok, so we left off on the dusty disk around Fomalhaut.