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"Based on its density, scientists think GJ 1214b is made up of about three-quarters liquid water with a solid core of iron and nickel and an atmosphere of hydro

by luchak 17y ago

"Based on its density, scientists think GJ 1214b is made up of about three-quarters liquid water with a solid core of iron and nickel and an atmosphere of hydrogen and helium—not unlike Earth." what This is either terrible writing or terrible science (on the author's part, not the scientists', I would imagine). About 70% of the Earth's surface is water, but only a fraction of a percent of Earth's mass is water. (http://bit.ly/7Gfk8V http://bit.ly/7Gfk8V, total water volume from http://en.wikipedia.org/wiki/Water#Water_on_Earth http://en.wikipedia.org/wiki/Water#Water_on_Earth). And the Earth's atmosphere is definitely not primarily hydrogen and helium.

jpwagner 17y ago
in theory, that sounds a lot more like Earth than any other known celestial body. now, whether or not it's all accurate, we'll find out eventually.
- luchak 17y ago
  I'm not so sure, given the article as written. Comparing Earth and Jupiter: 1. made up of about three-quarters liquid water False for both. Possibly true for Earth if you're talking about surface area, but that's a pretty generous interpretation of the article as written. 2. with a solid core of iron and nickel Likely true for both. ("At the center of [Jupiter's] rocky core is probably a metallic ball of iron and nickel, just like Earth's core." http://www.spacedaily.com/reports/Jupiter_Has_Large_Rocky_Core_Surrounded_By_Layer_Of_Ice_999.html http://www.spacedaily.com/reports/Jupiter_Has_Large_Rocky_Co...) 3. an atmosphere of hydrogen and helium True for Jupiter, not for Earth. That's 2 of 3 for Jupiter, 1 of 3 for Earth (or 2 of 3 for Earth if you're being generous). Mars sounds a lot more like Earth than GJ 1214b does, based on the article. GJ 1214b might be more like Earth than any other known exoplanet, but given the murky reporting it's hard to tell.
  - hugh_ 17y ago
    GJ 1214b might be more like Earth than any other known exoplanet, but given the murky reporting it's hard to tell. I'd say the most Earthlike exoplanet discovered so far is CoRoT-7b, discovered a few months ago. It's about five times more massive than Earth, but has a similar density, implying it should consist mostly of rock. http://spacefellowship.com/2009/09/16/smallest-exoplanet-is-shown-to-be-a-solid-rocky-world/ http://spacefellowship.com/2009/09/16/smallest-exoplanet-is-...
- hugh_ 17y ago
  Actually it'd be more like a small Neptune/Uranus than a large Earth. Those two planets are made up mostly of a water/ammonia/methane mixture with a solid core and a H/He outer atmosphere. http://en.wikipedia.org/wiki/Neptune#Composition_and_structure http://en.wikipedia.org/wiki/Neptune#Composition_and_structu...
- eru 17y ago
  Mars and Venus are more similar to Earth than this.
bioweek 17y ago
How do they know what it's made of? How do they even know the density?
- boredguy8 17y ago
  The gist: spectrum analysis of light that passes through the planet's atmosphere from the system's sun compared to light that doesn't pass through the planet's atmosphere. They look at what light bands the planet's atmosphere absorbed. (IANA astrophysicist, learn more at http://en.wikipedia.org/wiki/Absorption_spectrum http://en.wikipedia.org/wiki/Absorption_spectrum )
  - robryan 17y ago
    From what I understand though there are some assumptions made based off the readings to arrive at the description we have? As in the same spectrum differences could mean more than one thing?
  - bioweek 17y ago
    I thought the article said they looked at how the stars light was dimmed by the planet. They also managed to do a spectrum analysis?
    - hugh_ 17y ago
      No, they didn't -- getting the absorption spectrum of a transiting exoplanet is an order of magnitude or two beyond the capabilities of present-day instruments. They just measured the density. From the density, though, you can get a pretty good idea of what it looks like. There are three basic ingredients which go into making planets: rock (including pure metals), "ice" (a catch-all term which includes all phases of water along with methane and ammonia) and hydrogen/helium mixture. Everything else is too rare to worry about. Knowing (basically) the density of each of these components, plus knowing the fact that H/He mixture won't accrete to a body until its mass goes beyond a certain point, you can put pretty good constraints on what the composition of a planet of a certain mass and radius should be. Of course we could be wrong -- it could equally well be a ball of pure argon or something; however it's hard to imagine how any such thing would form.

by luchak 17y ago

jpwagner 17y ago

in theory, that sounds a lot more like Earth than any other known celestial body. now, whether or not it's all accurate, we'll find out eventually.

luchak 17y ago
I'm not so sure, given the article as written. Comparing Earth and Jupiter: 1. made up of about three-quarters liquid water False for both. Possibly true for Earth if you're talking about surface area, but that's a pretty generous interpretation of the article as written. 2. with a solid core of iron and nickel Likely true for both. ("At the center of [Jupiter's] rocky core is probably a metallic ball of iron and nickel, just like Earth's core." http://www.spacedaily.com/reports/Jupiter_Has_Large_Rocky_Core_Surrounded_By_Layer_Of_Ice_999.html http://www.spacedaily.com/reports/Jupiter_Has_Large_Rocky_Co...) 3. an atmosphere of hydrogen and helium True for Jupiter, not for Earth. That's 2 of 3 for Jupiter, 1 of 3 for Earth (or 2 of 3 for Earth if you're being generous). Mars sounds a lot more like Earth than GJ 1214b does, based on the article. GJ 1214b might be more like Earth than any other known exoplanet, but given the murky reporting it's hard to tell.
- hugh_ 17y ago
  GJ 1214b might be more like Earth than any other known exoplanet, but given the murky reporting it's hard to tell. I'd say the most Earthlike exoplanet discovered so far is CoRoT-7b, discovered a few months ago. It's about five times more massive than Earth, but has a similar density, implying it should consist mostly of rock. http://spacefellowship.com/2009/09/16/smallest-exoplanet-is-shown-to-be-a-solid-rocky-world/ http://spacefellowship.com/2009/09/16/smallest-exoplanet-is-...
hugh_ 17y ago
Actually it'd be more like a small Neptune/Uranus than a large Earth. Those two planets are made up mostly of a water/ammonia/methane mixture with a solid core and a H/He outer atmosphere. http://en.wikipedia.org/wiki/Neptune#Composition_and_structure http://en.wikipedia.org/wiki/Neptune#Composition_and_structu...
eru 17y ago
Mars and Venus are more similar to Earth than this.

bioweek 17y ago

How do they know what it's made of? How do they even know the density?

boredguy8 17y ago
The gist: spectrum analysis of light that passes through the planet's atmosphere from the system's sun compared to light that doesn't pass through the planet's atmosphere. They look at what light bands the planet's atmosphere absorbed. (IANA astrophysicist, learn more at http://en.wikipedia.org/wiki/Absorption_spectrum http://en.wikipedia.org/wiki/Absorption_spectrum )
- robryan 17y ago
  From what I understand though there are some assumptions made based off the readings to arrive at the description we have? As in the same spectrum differences could mean more than one thing?
- bioweek 17y ago
  I thought the article said they looked at how the stars light was dimmed by the planet. They also managed to do a spectrum analysis?
  - hugh_ 17y ago
    No, they didn't -- getting the absorption spectrum of a transiting exoplanet is an order of magnitude or two beyond the capabilities of present-day instruments. They just measured the density. From the density, though, you can get a pretty good idea of what it looks like. There are three basic ingredients which go into making planets: rock (including pure metals), "ice" (a catch-all term which includes all phases of water along with methane and ammonia) and hydrogen/helium mixture. Everything else is too rare to worry about. Knowing (basically) the density of each of these components, plus knowing the fact that H/He mixture won't accrete to a body until its mass goes beyond a certain point, you can put pretty good constraints on what the composition of a planet of a certain mass and radius should be. Of course we could be wrong -- it could equally well be a ball of pure argon or something; however it's hard to imagine how any such thing would form.