Featured Research

from universities, journals, and other organizations

Earth-like exoplanet in mass and size: While too hot to support life, Kepler 78b is roughly the size of Earth

Date:
October 30, 2013
Source:
Massachusetts Institute of Technology
Summary:
In August, researchers identified an exoplanet with an extremely brief orbital period: The team found that Kepler 78b, a small, intensely hot planet 400 light-years from Earth, circles its star in just 8.5 hours — lightning-quick, compared with our own planet's leisurely 365-day orbit. From starlight data gathered by the Kepler Space Telescope, the scientists also determined that the exoplanet is about 1.2 times Earth's size — making Kepler 78b one of the smallest exoplanets ever measured.

This illustration compares our Earth with the newly confirmed lava planet Kepler-78b. Kepler-78b is about 20 percent larger than Earth, with a diameter of 9,200 miles, and weighs roughly 1.8 times as much as Earth.
Credit: David A. Aguilar (CfA)

In August, MIT researchers identified an exoplanet with an extremely brief orbital period: The team found that Kepler 78b, a small, intensely hot planet 400 light-years from Earth, circles its star in just 8.5 hours -- lightning-quick, compared with our own planet's leisurely 365-day orbit. From starlight data gathered by the Kepler Space Telescope, the scientists also determined that the exoplanet is about 1.2 times Earth's size -- making Kepler 78b one of the smallest exoplanets ever measured.

Now this same team has found that Kepler 78b shares another characteristic with Earth: its mass. By analyzing the movement of its host star, Kepler 78, the scientists determined that the exoplanet is about 1.7 times as massive as Earth. From the same measurements, they calculated that the planet's density is 5.3 grams per cubic centimeter, closely resembling Earth's density (5.5 grams per cubic centimeter).

The findings make Kepler 78b the smallest exoplanet for which the mass and size are known. These new measurements provide strong evidence that Kepler 78b is composed mostly of rock and iron, similar to Earth.

However, that's where the similarities may end: The exoplanet, due to its extreme proximity to its star, is likely blazing at temperatures too high to support life.

"It's Earth-like in the sense that it's about the same size and mass, but of course it's extremely unlike the Earth in that it's at least 2,000 degrees hotter," says team member Josh Winn, an associate professor of physics at MIT and a member of the Kavli Institute for Astrophysics and Space Research. "It's a step along the way of studying truly Earth-like planets."

Winn and his colleagues, including lead author Andrew Howard, of the University of Hawaii, publish their results this week in the journal Nature. The group's results appear in the same issue as a paper published by a separate group in Geneva, reporting similar results -- scientific agreement that Winn says adds confidence to the mass measurement.

Watching for a wobble

Planets with extremely tight orbits offer scientists a wealth of data: For instance, each week Kepler 78b circles its star about 20 times, giving researchers numerous opportunities to observe its behavior.

The team previously determined Kepler 78b's orbit and size by analyzing the light given off by the star as the planet passes in front of it, or transits. The researchers detected a transit each time the star's light dipped, and measured this dimming to determine the planet's size. (The bigger an exoplanet, the more light it blocks.)

Measuring the planet's mass was a somewhat trickier endeavor. Instead of tracking the planet's motion, the researchers tracked the motion of the star itself. Depending on its mass, a planet can exert a gravitational tug on its star. This stellar motion can be detected as a very slight wobble, known as a Doppler shift.

Winn and his colleagues looked to measure Kepler 78's Doppler shift by analyzing observations from the Keck Observatory in Hawaii -- one of the largest telescopes in the world. The team analyzed starlight data taken over a period of eight days. Despite the telescope's strength, the signal from the star was incredibly faint, making a daunting task for the scientists.

"Each of the eight nights along the way, we were agonizing over it, whether it was worth continuing or not," Winn recalls.

Out, damn starspot

In addition to the challenge of picking out such tiny signals, the researchers had to contend with an effect that initially muddled the data: starspots, dark patches on the surface of stars. Graduate student Roberto Sanchis-Ojeda, who has studied the effect of starspots on exoplanet detection, says the troublesome patches can make a star's Doppler shift appear larger, dramatically complicating scientists' calculations of a planet's mass.

Sanchis-Ojeda was able to solve this puzzle by taking into account Kepler 78's rotational period. By tracking the frequency at which certain starspots reappeared, Sanchis-Ojeda determined that the star completes a full rotation every 12.5 days -- considerably longer than the planet's orbital period of 8.5 hours. From these measurements, Sanchis-Ojeda was able to calculate the star's true Doppler shift.

From his calculations, Sanchis-Ojeda found that the star rotates relatively slowly, at 1.5 meters per second -- about the speed of a jog, or a brisk walk.

"The star is moving at the same speed as when we walk to school or go grocery shopping," Sanchis-Ojeda notes. "The difference is that this star is 400 light-years away, so imagine how complicated it is to measure such speeds from so far away."

From the star's Doppler shift, the team determined that Kepler 78b's mass is 1.7 times that of Earth -- a measurement that suggests the planet is made mostly of rock and iron. Such a composition, Winn says, is not surprising, given the planet's extremely close proximity to its star. A less massive planet, such as one made entirely of gas, would not be able to hold together in such a tight orbit.

While its similarities to Earth likely end with Kepler 78b's size and mass, Winn says there is still more to learn about the planet, such as its surface and atmospheric composition -- a goal that the group plans to pursue next.

Co-authors on the paper include researchers from the University of Hawaii, the University of California at Berkeley, the Harvard-Smithsonian Center for Astrophysics, the University of California at Santa Cruz, and Yale University.

This research received support from NASA and the Kepler Participating Scientist Program.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Jennifer Chu. Note: Materials may be edited for content and length.


Journal Reference:

  1. Andrew W. Howard, Roberto Sanchis-Ojeda, Geoffrey W. Marcy, John Asher Johnson, Joshua N. Winn, Howard Isaacson, Debra A. Fischer, Benjamin J. Fulton, Evan Sinukoff, Jonathan J. Fortney. A rocky composition for an Earth-sized exoplanet. Nature, 2013; DOI: 10.1038/nature12767

Cite This Page:

Massachusetts Institute of Technology. "Earth-like exoplanet in mass and size: While too hot to support life, Kepler 78b is roughly the size of Earth." ScienceDaily. ScienceDaily, 30 October 2013. <www.sciencedaily.com/releases/2013/10/131030142815.htm>.
Massachusetts Institute of Technology. (2013, October 30). Earth-like exoplanet in mass and size: While too hot to support life, Kepler 78b is roughly the size of Earth. ScienceDaily. Retrieved April 16, 2014 from www.sciencedaily.com/releases/2013/10/131030142815.htm
Massachusetts Institute of Technology. "Earth-like exoplanet in mass and size: While too hot to support life, Kepler 78b is roughly the size of Earth." ScienceDaily. www.sciencedaily.com/releases/2013/10/131030142815.htm (accessed April 16, 2014).

Share This



More Space & Time News

Wednesday, April 16, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA Showcases Lunar Eclipse

NASA Showcases Lunar Eclipse

AP (Apr. 15, 2014) Star gazers in parts of North and South America got a rare treat early Tuesday morning - a total eclipse of the moon. (April 15) Video provided by AP
Powered by NewsLook.com
Spacecrafts Could Use Urine As Fuel Source

Spacecrafts Could Use Urine As Fuel Source

Newsy (Apr. 15, 2014) New research says the urea from urine could be recycled for fuel. Urea is filtered out of wastewater when making drinking water. Video provided by Newsy
Powered by NewsLook.com
NASA Approves Mon. Space Station Supply Launch

NASA Approves Mon. Space Station Supply Launch

AP (Apr. 13, 2014) NASA decided Sunday to stick with the planned launch of the SpaceX cargo ship, despite a critical computer outage at the space station.Liftoff is scheduled for 4:58 p.m. Monday from Cape Canaveral. (April 13) Video provided by AP
Powered by NewsLook.com
'Blood Moon' Attracts Stargazers, Conspiracy Theories

'Blood Moon' Attracts Stargazers, Conspiracy Theories

Newsy (Apr. 13, 2014) Tuesday's total lunar eclipse will bring out both stargazers and conspiracy theorists alike as the blood red moon fills up the early morning sky. 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