Featured Research

from universities, journals, and other organizations

Are super-Earths actually mini-Neptunes?

Date:
February 4, 2013
Source:
Royal Astronomical Society (RAS)
Summary:
In the last two decades astronomers have found hundreds of planets in orbit around other stars. One type of these so-called 'exoplanets' is the super-Earths that are thought to have a high proportion of rock but at the same time are significantly bigger than our own world. Now a new study suggests that these planets are actually surrounded by extended hydrogen-rich envelopes and that they are unlikely to ever become Earth-like. Rather than being super-Earths, these worlds are more like mini-Neptunes.

A diagram comparing the Earth, at left, to a cross-section of a super-Earth on the right. The super-Earth has a relatively small rocky core, an atmosphere of methane, water and hydrogen and an extended hydrogen envelope.
Credit: H. Lammer

In the last two decades astronomers have found hundreds of planets in orbit around other stars. One type of these so-called 'exoplanets' is the super-Earths that are thought to have a high proportion of rock but at the same time are significantly bigger than our own world. Now a new study led by Helmut Lammer of the Space Research Institute (IWF) of the Austrian Academy of Sciences suggests that these planets are actually surrounded by extended hydrogen-rich envelopes and that they are unlikely to ever become Earth-like. Rather than being super-Earths, these worlds are more like mini-Neptunes.

The scientists publish their work in the journal Monthly Notices of the Royal Astronomical Society.

'Super-Earths' follow a different evolutionary track to the planets found in our Solar system but an open question is whether they can evolve to become rocky bodies like the 'terrestrial planets' Mercury, Venus, Earth and Mars. To try to answer this, Dr Lammer and his team looked at the impact of radiation on the upper atmospheres of super-Earths orbiting the stars Kepler-11, Gliese 1214 and 55 Cancri.

This group of planets are all a few times more massive and slightly larger than Earth. They orbit very close to their respective stars. The way in which the mass of planets scales with their sizes suggests that they have solid cores surrounded by hydrogen or hydrogen-rich atmospheres, probably captured from the clouds of gas and dust (nebulae) from which the planets formed.

The new model suggests that the short wavelength extreme ultraviolet light (much 'bluer' than the blue light we see with our eyes) of the host stars heats up the gaseous envelopes of these worlds, so that they expand up to several times the radius of each planet and gas escapes from them fairly quickly. Nonetheless most of the atmosphere remains in place over the whole lifetime of the stars they orbit.

"Our results indicate that, although material in the atmosphere of these planets escapes at a high rate, unlike lower mass Earth-like planets many of these super-Earths may not get rid of their nebula-captured hydrogen-rich atmospheres," says Dr Lammer.

Rather than becoming more like Earth, the super-Earths may more closely resemble Neptune, which together with Uranus, is a smaller 'gas giant' in our Solar system. If the scientists' results are right, then super-Earths further out from their stars in the 'habitable zone', where the temperature would allow liquid water to exist, would hold on to their atmospheres even more effectively. If that happens, they would be much less likely to be habitable.

The team's findings will be put to the test in 2017 when the European Space Agency launches the CHaracterising ExOPlanets Satellite (CHEOPS). This will study super-Earths in more detail and should be able to tell whether some of these exotic worlds could one day be more like our own.


Story Source:

The above story is based on materials provided by Royal Astronomical Society (RAS). Note: Materials may be edited for content and length.


Journal Reference:

  1. Helmut Lammer, N. V. Erkaev, P. Odert, K. G. Kislyakova, M. Leitzinger, M. L. Khodachenko. Probing the blow-off criteria of hydrogen-rich 'super-Earths'. Monthly Notices of the Royal Astronomical, 2013; DOI: 10.1093/mnras/sts705

Cite This Page:

Royal Astronomical Society (RAS). "Are super-Earths actually mini-Neptunes?." ScienceDaily. ScienceDaily, 4 February 2013. <www.sciencedaily.com/releases/2013/02/130204094652.htm>.
Royal Astronomical Society (RAS). (2013, February 4). Are super-Earths actually mini-Neptunes?. ScienceDaily. Retrieved September 22, 2014 from www.sciencedaily.com/releases/2013/02/130204094652.htm
Royal Astronomical Society (RAS). "Are super-Earths actually mini-Neptunes?." ScienceDaily. www.sciencedaily.com/releases/2013/02/130204094652.htm (accessed September 22, 2014).

Share This



More Space & Time News

Monday, September 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA's MAVEN Spacecraft Has Finally Reached Mars

NASA's MAVEN Spacecraft Has Finally Reached Mars

Newsy (Sep. 22, 2014) After a 10-month voyage through space, NASA's MAVEN spacecraft is now orbiting the Red Planet. Video provided by Newsy
Powered by NewsLook.com
Raw: SpaceX Rocket Carries 3-D Printer to Space

Raw: SpaceX Rocket Carries 3-D Printer to Space

AP (Sep. 22, 2014) A SpaceX Rocket launched from Cape Canaveral, carrying a custom-built 3-D printer into space. NASA envisions astronauts one day using the printer to make their own spare parts. (Sept. 22) Video provided by AP
Powered by NewsLook.com
SpaceX Cargo Ship Blasts Off Toward Space Station

SpaceX Cargo Ship Blasts Off Toward Space Station

AFP (Sep. 21, 2014) SpaceX's unmanned Dragon cargo ship blasts off toward the International Space Station, carrying a load of supplies and science experiments for the astronauts living there. Duration: 00:35 Video provided by AFP
Powered by NewsLook.com
NASA's MAVEN To Study Martian Atmosphere

NASA's MAVEN To Study Martian Atmosphere

Newsy (Sep. 21, 2014) NASA's Maven will soon give information that could explain what happened to Mars' atmosphere. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins