Featured Research

from universities, journals, and other organizations

Forming Super-Earths By Ultraviolet Stripping

Date:
June 7, 2006
Source:
Carnegie Institution
Summary:
A new explanation for forming "super-Earths" suggests that they are more likely to be found orbiting red dwarf stars -- the most abundant type of star -- than gas giant planets like Jupiter and Saturn. Dr. Alan Boss of the Carnegie Institution's Department of Terrestrial Magnetism, describes a mechanism whereby UV radiation from a nearby massive star strips off a planet's gaseous envelope exposing a super-Earth. The work is published in the June 10, 2006, Astrophysical Journal (Letters).

Four Jupiter-mass clumps formed on Saturn-like orbits after 215 years of evolution of an initially smooth disk of gas and dust in orbit around a red dwarf star with a mass half that of our Sun. Purple denotes regions with high gas density in the midplane of the planet-forming disk, while red regions denote low gas density. The red dwarf lies unseen at the center of the disk. These protoplanets would all be stripped down to super-Earths if this planetary system formed close to a massive star.
Credit: Image courtesy of Carnegie Institution

A new explanation for forming "super-Earths" suggests that they are more likely to be found orbiting red dwarf stars -- the most abundant type of star -- than gas giant planets like Jupiter and Saturn. The theory, by Dr. Alan Boss of the Carnegie Institution's Department of Terrestrial Magnetism, describes a mechanism whereby UV radiation from a nearby massive star strips off a planet's gaseous envelope exposing a super-Earth. The work, published in the June 10, 2006, Astrophysical Journal (Letters), explains recent extrasolar planet discoveries by the microlensing method.

Related Articles


Super-Earths have masses that range between those of Earth and Neptune but have unknown compositions. "Of the 300 stars closest to the Sun, at least 230 are red dwarf stars, with masses less than half that of our Sun," Boss says. "Because nearby stars are the easiest places to look for other Earth-like planets, it is important to try to predict what types of planetary systems they might have, and that means trying to figure out how their planets can form."

Recently, evidence was presented for perhaps the lowest-mass planet found to date in orbit around a main sequence star like the Sun. It was found by an international consortium of astronomers via a microlensing event, where a foreground star amplifies the light from a much more distant star by bending the light of the background star in our direction, an effect predicted by Einstein. In addition, they observed a secondary brightening as well, consistent with the presence of a roughly 5.5-Earth-mass planet orbiting the foreground star at a distance similar to the asteroid belt in our Solar System. While the identity of the foreground star is unknown, it is most likely a red dwarf (M dwarf) star. Evidence for microlensing by a 13-Earth-mass planet around another red dwarf was subsequently presented.

The microlensing detection teams interpreted their discoveries as evidence that super-Earths can form around red dwarf stars by the same process that led to the formation of the Earth and other terrestrial planets in our Solar System, namely collisions between progressively larger solid bodies. This process is so slow, however, that it is unlikely to lead to the formation of gas giant planets around red dwarfs, because the disk gas is likely to disappear before the solid bodies can grow large enough to capture any gas. However, microlensing teams had previously found evidence for two gas giant planets with masses similar to that of Jupiter around two other red dwarf stars. Given that equal numbers of both giant and super-Earth-massed planets have been detected by microlensing, yet the former are easier to detect, they argued that there must be far fewer giant planets than super-Earths.

Boss was pondering these discoveries while sitting in a hotel lobby in Houston when a new explanation for the four microlensing planets occurred to him. He had previously shown that red dwarf stars are likely to form gas giant protoplanets rapidly by the disk instability mechanism, whereby the gaseous disk forms spiral arms and self-gravitating protoplanets that would become Jupiters in the absence of any interference. However, most stars form in regions where massive O stars eventually form. Such stars emit immense amounts of ultraviolet (UV) radiation, which strips off the disk gas around young stars, exposing their outer protoplanets to UV and stripping away their gaseous envelopes. In 2002 Boss and his Carnegie colleagues, George Wetherill and Nader Haghighipour (now at the University of Hawaii), proposed this explanation for forming Uranus and Neptune, which have masses similar to those of the super-Earths.

"It dawned on me that because UV stripping depends on the mass of the central star, super-Earths should be found on much smaller orbits around a red dwarf than around the Sun," Boss says. "This idea naturally predicts red dwarfs that form close to massive stars will end up with super-Earths orbiting at the distances where super-Earths have been found by microlensing." Red dwarfs that form in the absence of massive stars will not suffer UV stripping and hence will form gas giant planets at these distances, instead of super-Earths. Such stars are in the minority so red dwarfs should be orbited mostly by super-Earths at asteroidal distances and beyond. This prediction agrees with the microlensing detections to date.

It remains to be seen if Boss's theoretical predictions will be verified by the ongoing microlensing searches and by the space-based planet detection missions being planned by NASA and the European Space Agency. Determining the compositions of super-Earths will be a major challenge with important implications for their habitability.

The calculations were performed on the Carnegie Alpha Cluster of workstations at DTM, the purchase of which was supported in part by a grant from the National Science Foundation's Major Research Instrumentation program. Boss' research on planet formation is supported in part by NASA's Planetary Geology & Geophysics and Origins of Solar Systems Programs, and by the NASA Astrobiology Institute (NAI). The NAI, founded in 1997, is a partnership between NASA, 16 major U.S. teams and six international consortia. NAI's goal is to promote, conduct, and lead integrated multidisciplinary astrobiology research and to train a new generation of astrobiology researchers. For more information about the NAI on the Internet, visit: http://nai.nasa.gov/

The Department of Terrestrial Magnetism is part of the Carnegie Institution of Washington (www.CarnegieInstitution.org), which has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.


Story Source:

The above story is based on materials provided by Carnegie Institution. Note: Materials may be edited for content and length.


Cite This Page:

Carnegie Institution. "Forming Super-Earths By Ultraviolet Stripping." ScienceDaily. ScienceDaily, 7 June 2006. <www.sciencedaily.com/releases/2006/06/060607171721.htm>.
Carnegie Institution. (2006, June 7). Forming Super-Earths By Ultraviolet Stripping. ScienceDaily. Retrieved April 2, 2015 from www.sciencedaily.com/releases/2006/06/060607171721.htm
Carnegie Institution. "Forming Super-Earths By Ultraviolet Stripping." ScienceDaily. www.sciencedaily.com/releases/2006/06/060607171721.htm (accessed April 2, 2015).

Share This


More From ScienceDaily



More Space & Time News

Thursday, April 2, 2015

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

The Universe Could Be Full Of Tatooine Sunsets

The Universe Could Be Full Of Tatooine Sunsets

Newsy (Mar. 30, 2015) — University of Utah researchers say mathematical simulations show small, rocky planets, like Tatooine from "Star Wars," can form in dual-star systems. Video provided by Newsy
Powered by NewsLook.com
What NASA Wants To Learn From Its 'Year In Space' Tests

What NASA Wants To Learn From Its 'Year In Space' Tests

Newsy (Mar. 28, 2015) — Astronaut Scott Kelly and cosmonaut Mikhail Kornienko will spend a year in space running tests on human physiology and psychology. Video provided by Newsy
Powered by NewsLook.com
Raw: Astronauts Arrive at ISS for 1-Year Mission

Raw: Astronauts Arrive at ISS for 1-Year Mission

AP (Mar. 28, 2015) — The capsule carrying a Russian and an American who are to spend a year away from Earth docked Saturday with the International Space Station. (March 28) Video provided by AP
Powered by NewsLook.com
Crew Starts One-Year Space Mission

Crew Starts One-Year Space Mission

Reuters - News Video Online (Mar. 28, 2015) — Russian-U.S. crew arrives safely at the International Space Station for the start of a ground-breaking year-long stay. Paul Chapman reports. Video provided by Reuters
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:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

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