Astronomy.com blog : Daniel Pendick, exoplanets

Low-mass extrasolar planets aplenty

Daniel Pendick — Wed, 22 Apr 2009 21:14:00 GMT

Tuesday at the European Week of Astronomy and Space Science meeting in Hatfield, England, astronomers announced a new milestone: an extrasolar planet with the lowest confirmed mass of any yet discovered around a normal star.

“Confirmed” . . . “normal star” . . . seems like a lot of caveats, doesn’t it? Let me explain.

The planet is called Gliese 581 e, and the research says it contains 1.9 times Earth’s mass. Earth-mass planets are the holy grails of extrasolar studies right now. That’s because planets about the size and (rocky) composition of Earth — assuming the right surface conditions and the presence of liquid water — could potentially give rise to life in a form that would be familiar to us. You know, biological bug-eyed monster-type thingies. Or at least a brightly colored slime mold or bacterial colony.

The caveats gum up the works a bit, but they are essential. For instance, it’s important to include “confirmed,” because there is an unconfirmed contender for the lightweight-earthlike-exoplanet crown: MOA-2007-BLG-192-L b.

This little guy might be a mere 1.4 Earth masses, but that depends on certain assumptions being correct — like estimates of how big the planet’s parent star is. The mass of the star could affect the calculated mass of MOA-2007-BLG-192-L b.

And it’s also important to say “normal star” because smaller and lighter planets exist around decidedly abnormal stars called pulsars. A pulsar is the superdense core of an aged star that spins rapidly, causing energy radiating from hotspots on the star to appear to pulsate as seen from a distance, as if you were watching a faraway lighthouse. One known pulsar, called PSR B1620-26, hosts a planet significantly LESS massive than Earth.

The downside for science writers is that when reporting biggest/smallest/fastest scientific discoveries, those caveats sure get in the way of a snappy headline. But in science, the caveats are everything. Scientists are obsessively precise about their claims. They have to be. It’s what we pay them to do – to be careful.

We struggle every day with how to handle those caveats. We want to describe discoveries in the most simple, direct, and clear way possible. But to be accurate, we have to find ways to sneak in the important caveats without tripping up the reader. It’s hard to do, but never impossible.

My first editor — um, let me qualify that: my first editor at a paying professional science-writing job — assured me that the English language is powerful and flexible enough to solve any problem. You just have to work hard to find that perfect turn of phase, that vivid verb, or that ideal sentence structure that does the job.

But I wonder if she ever had to write about low-mass exoplanets.

Fomalhaut exoplanet discovery Q&A with NASA scientist

Daniel Pendick — Thu, 13 Nov 2008 19:33:00 GMT

The discovery and optical imaging of Fomalhaut b, a planet orbiting the nearby star Fomalhaut, has wider implications for exoplanet science. I talked to NASA scientist Marc Kuchner about it. Kuchner works in the Exoplanets and Stellar Astrophysics Laboratory at Goddard Space Flight Center in Greenbelt, Maryland. He uses computer models to study the effect planets have on interplanetary dust.

Kuchner (pictured at left below) and Christopher Stark, a graduate physics student at University of Maryland, recently published a study showing that a planet nearly as small as Mars could carve rings and other structures in interplanetary dust that telescopes on Earth could detect — even if the planet is too small to see directly. Here’s what Kuchner had to say:

Pendick: Tell us a little about your work on exoplanets.

Kuchner: I do computer modeling and high precision observations of planetary systems. My primary focus is predicting how planetary systems will appear in images, like the ones reported in the press releases this week, and coming up with new ways to image them myself. So you could say I'm one of the main competitors of the teams reporting this week's discoveries. My theoretical predictions include the shapes of debris disks and the compositions of planets. My observational work has focused on new techniques that create the high contrast and high angular resolution needed to image planetary systems directly: coronography and interferometry.

Pendick: What was your first reaction to hearing that your colleagues had imaged an actual exoplanet?

Kuchner: There have been some other images of objects that may well be exoplanets. But this is the first time we have witnessed a planet orbiting a star. That's powerful!

I think that this discovery, along with some others soon to be announced, marks the beginning of a new era — a time when we can look at other planetary systems and see extrasolar versions of our own solar system, like looking in the mirror.

New York Times columnist Thomas Friedman, commenting on the progress of globalization, and the remarkable way our lives are connected to those across the ocean, titled his book The world is flat. Now we are seeing new worlds across another kind of ocean, the space between our solar system and other planetary systems. I'm starting to think, "The universe is flat.”

Pendick: Can you expand a little on those “other images of objects that may well be exoplanets”? Which do you mean?

Kuchner: There have been several good planet candidates detected by direct imaging. Some of them have turned out to be a bit more massive than what most people consider to be the upper limit of planethood. The best candidate before Fomalhaut b is probably 2M1207b, an object with a mass of about 4 Jupiter masses orbiting the brown dwarf star 2M1207 in the constellation Centaurus, about 170 light-years from Earth.

Pendick: We recently covered a study in the magazine claiming that the Gemini North Telescope imaged an 8-Jupiter-mass planet. Should I consider that a really big planet or just a really small star?

Kuchner: With that mass, you would have to call it planet, not a small star. But in general, it’s hard to determine the mass of a planet in a direct image like that, just as you can’t tell the weight of a carton just by looking at it. And unlike the Fomalhaut planet, the Gemini planet candidate was not yet observed to orbit its star. There’s a chance it might just be a background object.

Also, in between those two categories (star and planet), there is a class of objects called brown dwarfs that are like stars in some ways and like planets in other ways. Some planet candidates have turned out to brown dwarfs.

Pendick: The other thing I’m wondering about is possible parallels or differences between the Fomalhaut discovery and your computer modeling work on detecting small planets — perhaps too small for direct imaging — and their effect on interplanetary dust.

It seems that large structures, such as sharp-edged dust rings, could help astronomers target other solar systems for closer study so that we may image and study the actual planets. The dust structures then become a sort of giant billboard saying, “Planet this way!” Is that the common message of your modeling work and the Fomalhaut discovery?

Kuchner: Yes, that's exactly it. Dust rings are the signposts of planetary systems. They are much brighter than planets, and when we see them, we know that there's something interesting going on. Sometimes they even seem to point to right where the planets are located.

Pendick: If rings point the way, how do we observe rings? Does it always work best at the longer wavelengths? For Fomalhaut, it seems they first observed the ring in submillimeter wavelengths. How else will we be able to find the rings? Infrared? Other?

Kuchner: For these kinds of rings, it's often easier to spot them at longer wavelengths, say, the mid-infrared or submillimeter, where they shine in thermal radiation, and where the star they orbit is relatively faint. To see them in visible light, you need to block out the light from the star somehow (for example, using a coronagraph, as Kalas and his colleagues did when they imaged the planet orbiting Fomalhaut).

There are a few new telescopes coming online in the next decade that should be fantastic for finding and imaging these rings: James Webb Space Telescope (JWST), which works in the infrared, and Atacama Large Millimeter Array (ALMA), operating in the submillimeter range (between infrared and radio wavelengths).

I'm hoping we'll also be able to fly the Terrestrial Planet Finder (TPF), which will use the latest in coronagraph technology to block out the starlight. It will allow us to look for rings much closer to the star, in the habitable zone where we might see earthlike planets.

Extra! Extra! Hobbit solar system discovered!

Daniel Pendick — Wed, 21 Nov 2007 19:16:00 GMT

They've discovered Earth ... again.

The astronomy blogosphere is abuzz with news of "shrunken versions of our solar system" and "miniature worlds in the making," at least according to the press releases I've been reading. Nobody has called them "Hobbit solar systems" yet, but give them time.

Alexander Scholz of the University of St. Andrews in Scotland, and Ray Jayawardhana from the University of Toronto reported discovery of 18 planet-mass objects (planemos) in a star cluster in Orion. Planemos form by the collapse of gas and dust, but they are not massive enough to initiate nuclear fusion and become suns.

Planemos were discovered about the year 2000. Astronomers thought they were either young planets booted out of their solar systems or small stars that failed to ignite. Astronomy has covered the story for years, of course.

In a paper to be published in Astrophysical Journal Letters, Scholz and Jayawardhana describe some important new observations with the Spitzer Space Telescope. The star cluster with the planemos is only 3 million years old, an appropriate time for making new Earths.

And about a third of the planemos are encircled by dusty disks of the type one would expect to see in a star system capable of forming — you guessed it — planets. And not just any old planets; rocky, terrestrial, Earth-like planets.

Also this week, another team reported strong evidence of a dusty, planet-forming disk around the star HD 23514 in the Pleiades star cluster (M45), also in Orion. Apparently, Orion the Hunter knows a lot about birthin' babies.

We can see these systems only because of powerful instruments like Spitzer, which can detect the heat emitted by dusty disks. The objects are essentially invisible in other wavelengths of light. So, kudos (again and again and again) to the Spitzer Space Telescope.

This is all fascinating stuff, but I can't help grinding an old axe: the tendency of the media to frame any new discovery regarding exoplanets in terms of how much they are like or unlike Earth. As I said in an earlier blog kvetching about the media's Earth-obsessed exoplanet coverage:

Gosh, it's just like home! You can't swing a dead cat around the media coverage of Gliese 581C without hitting the word Earth. Earth-like. Super-Earth. Earth-like life. Earth twin. Sister planet. Earth-like conditions. Earth 2. The climate in exoplanet science is positively Earth-centric.

Take the new planemos. If they develop rocky planets, just how Earth-like are they likely to be, besides being solid? Not much like Earth, I suspect. They would lie forever in near pitch-darkness, frozen, barren. As Elton John's Rocket Man might have said, a Hobbit exoplanet ain't the kind of place to raise your kids.

So, let's skip all the Earth talk. The really amazing point is that it looks more and more likely that the universe is just bursting at the seams with planetary systems. If even a small fraction of those planets are in reasonably stable orbits, then the universe could be bursting at the seams with life, too. When you stop to consider that, who needs this "just like Earth" stuff to sell a story?