Exoplanet may have metal-rich atmosphere

Mar 16, 2011 By Jon Voisey, Universe Today
Artist’s impression of GJ 1214b. Credit: NASA

At first glance, GJ 1214b is just another of the growing number of the super-Earth class of exoplanets. Discovered by the MEarth Project in 2009, it orbits an M dwarf in Ophiuchus in a tight orbit, swinging the planet around every 1.6 days. Late last year, GJ 1214b became the first super-Earth to have a component of its atmosphere detected when astronomers compared its spectra to models finding broad agreement with water vapor present. New work, done by the same team, further refines the atmosphere’s potential characteristics.

Previously, the team suggested that their observations could potentially fit with two hypothetical planet models. In the first, the planet could be covered in hydrogen and helium, but the lack of absorption features in the ’s spectra suggested that this were not the case unless this layer were hidden by thick clouds. However, from the data available, they could not conclusively rule out this possibility.

Combining their old observations with more recent ones from the MEarth Observatory, the team now reports that they have been able to rule out this scenario with a 4.5 σ confidence (over 99.99%). The result of this is that the remaining model, which contains higher amounts of "metals" (astronomy speak meaning all elements with atomic numbers higher than helium). The team also continues to support their earlier conclusion that the atmosphere is most likely at least 10% water vapor by volume, stating this with a 3 σ (or 99.7%) confidence based on the new observations. While may sound give the impression of being an inviting place for a tropical jungle, the team predicts the close orbiting planet would be a sweltering 535 degrees Fahrenheit.

While these findings are interesting stories of the atmosphere, the prevalence of such heavy elements may also give information relating to the structure and history of the planet itself. Models of planetary atmosphere suggest that, for of the mass and temperature expected for GJ 1214b, there are two primary formation scenarios. In the first, the atmosphere is directly accreted during the planet’s formation. However, this would indicate a hydrogen rich atmosphere and has been ruled out. The second is that the planet formed further out, beyond the “snow line”, as an icy body, but moved in after formation, creating the atmosphere from sublimated ices.

Although outside of the scope of their atmospheric research, the team also used the timing of the transits to search for wobbles in the orbit that could be caused by additional planets in the system. Ultimately, none were discovered.

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Royale
2.3 / 5 (3) Mar 16, 2011
Wow. That byline is nuts. They say metal rich, then go on to explain everything higher than helium is considered "metal". So, oxygen is a metal. Neon, carbon, and anything that isn't hydrogen or helium.
Does this mean that the 10% water vapor gives the atmosphere 10% more metal? The atomic number of H2O would have to be greater than H or He, right?
yyz
4.6 / 5 (9) Mar 16, 2011
"Wow. That byline is nuts. They say metal rich, then go on to explain everything higher than helium is considered "metal". So, oxygen is a metal. Neon, carbon, and anything that isn't hydrogen or helium."

Different sciences use the term 'metal' differently. In astrophysics, elements heavier than hydrogen or helium (which are primarily primordial in origin) are referred to as 'metals'.

These heavier elements (atomic numbers 3-118) were produced by nucleosynthesis in stars and supernovae.

It should be noted the concept of a metal in the usual chemical sense is irrelevant in stars, as the chemical bonds that give elements their properties cannot exist at stellar temperatures.
Royale
1 / 5 (2) Mar 16, 2011
Aren't we talking about an exoplanet here? I completely understand what you're saying, but 535 degrees F is not nearly enough to melt metal. I get that it's just astrophysics terminology and they're not going to change, but maybe a release to the public should take that into consideration? Or perhaps the article writers should, and that's a whole different story... (Thinking out loud here).
omatumr
1.8 / 5 (5) Mar 16, 2011
Yes, astronomers usually refer to all elements heavier that H and He as metals.

That includes Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, . . . . . U
for elements #3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, . . . . . 92

Most astronomers do not yet agree that H and He in stellar atmospheres are simply brightly glowing waste products from the compact, energetic stellar core:

"Neutron repulsion," The APEIRON Journal, in press (2011) 19 pages

http://arxiv.org/...2.1499v1
yyz
3 / 5 (2) Mar 16, 2011
"I get that it's just astrophysics terminology and they're not going to change, but maybe a release to the public should take that into consideration? Or perhaps the article writers should..."

from the article:

"...contains higher amounts of "metals" (astronomy speak meaning all elements with atomic numbers higher than helium)."

Mebbe the author (who has a degree in astronomy) could have expanded on it a bit, though.
Gopper
1 / 5 (2) Mar 16, 2011
so i take it since they didnt elaborate on what metal is in the atmosphere that they dont know
yyz
5 / 5 (1) Mar 16, 2011
"so i take it since they didnt elaborate on what metal is in the atmosphere that they dont know"

After looking at many computer models of possible atmospheres that would be reasonably consistent with their observations, the team came to the conclusion that an atmosphere containing elements heavier than H or He was required.

While they are not able to discriminate between possible *metals*, water vapor (H2O) is expected to be "a dominant species" in the atmosphere of GJ 1214b.

See: http://arxiv.org/...70v1.pdf
(pg 7)

soulman
5 / 5 (1) Mar 17, 2011
Exoplant may have metal-rich atmosphere

Going by that title, I thought this article would be about Triffids!

(okay, so the Triffids weren't necessarily of extraterrestrial origin...)
malamucika13
Mar 17, 2011
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