Featured Research

from universities, journals, and other organizations

Origin and maintenance of a retrograde exoplanet

Date:
January 25, 2013
Source:
National Astronomical Observatory of Japan
Summary:
Astronomers have shown that the HAT-P-7 planetary system, which is about 1040 light-years from Earth in the constellation Cygnus, includes at least two giant planets and one companion star. The discovery of a previously unknown companion (HAT-P-7B) to the central star (HAT-P-7) as well as confirmation of another giant planet (HAT-P-7c) orbiting outside of the retrograde planet HAT-P-7b, offer new insights into how retrograde planets may form and endure.

Artist’s rendition of the HAT-P-7 system. Researchers used rhe Subaru Telescope to discover the retrograde planet (nearest the central star), another giant planet (in the foreground), and a companion star (upper right) in this system.
Credit: NAOJ

Astronomers have used the Subaru Telescope to show that the HAT-P-7 planetary system, which is about 1040 light-years from Earth in the constellation Cygnus, includes at least two giant planets and one companion star. The discovery of a previously unknown companion (HAT-P-7B) to the central star (HAT-P-7) as well as confirmation of another giant planet (HAT-P-7c) orbiting outside of the retrograde planet HAT-P-7b, offer new insights into how retrograde planets may form and endure.

Related Articles


A Japanese collaboration led by Norio Narita (National Astronomical Observatory of Japan) used the Subaru Telescope in 2008 to discover the first evidence of a retrograde orbit of an extrasolar planet, HAT-P-7b. Although retrograde planets, which have orbits that run counter to the spin of their central stars, are absent in our solar system, they occur in other planetary systems in the universe. However, scientists did not know how such retrograde planets formed.

Since his team's initial discovery of the retrograde planet HAT-P-7b, Narita has pursued his quest to explain its origin. As participants in the SEEDS (Strategic Exploration of Exoplanets and Disks with the Subaru Telescope) Project, he and his colleagues, Yasuhiro Takahashi, Masayuki Kuzuhara, and Teruyuki Hirano (all from the University of Tokyo), took high contrast images of the HAT-P-7 system with HiCIAO (High Contrast Instrument for the Subaru Next Generation Adaptive Optics) to develop a more complete picture of it.

The team first discovered two companion candidates around the HAT-P-7 system in 2009 and measured their proper motion over a three-year period until 2012. They confirmed that one of the two candidates is a common proper motion stellar companion to HAT-P-7, named HAT-P-7B.

The team also confirmed a long-term radial velocity trend for HAT-P-7. This indicated the existence of another giant planet, HAT-P-7c, orbiting between the orbits of HAT-P-7b (the retrograde planet) and HAT-P-7B (the stellar companion).

The question remained: How did the retrograde orbit of the planet develop?

In a 2012 research report, Dr. Simon Albrecht pointed out that certain gravitational effects between the central star and HAT-P-7b would prevent the long-term maintenance of its retrograde orbit. The current team thinks that the existence of the companion star (HAT-P-7B) and the newly confirmed outer planet (HAT-P-7c) are likely to play an important role in forming and maintaining the retrograde orbit of the inner planet (HAT-P-7b) via the Kozai mechanism, a long-term process during which a more massive object has an effect on the orbit of another. In the case of HAT-P-7b, the team posited so-called "sequential Kozai migration" as an explanation of this retrograde planet. They suggest that the companion star (HAT-P-7B) first affected the orbit of the newly confirmed outer planet (HAT-P-7c) through the Kozai mechanism, causing it to tilt. When the orbit of that planet inclined enough, HAT-P7c altered the orbit of the inner planet (HAT-P-7b) through the Kozai mechanism, so that it became retrograde. This sequential orbital evolution of the planet is one of the scenarios that could explain the origin of retrograde/tilted/eccentric planets.

Narita's team has demonstrated the importance of conducting high-contrast direct imaging observations for known planetary systems to check for the presence of outer faint companions, which may play an important role in understanding the entire picture of planetary migration. The findings provide important clues for understanding the origin of a variety of planetary systems, including those with highly tilted and eccentric orbits.

Notes

1) A retrograde planet is a planet with an orbit that runs counter (over 90 degrees) to the direction of the spin of the central star. Previous observations have revealed that about a third of hot Jupiters, exoplanets with characteristics similar to Jupiter but orbiting very close to their host stars, have tilted or even retrograde orbits relative to the spin of their central star.

2) The letters after the name of a star are consistent ways that astronomers label parts of a planetary system. The planetary system is named for the central star (HAT-P-7), and a companion star is labeled with an upper case B (HAT-P-7B). The first planet discovered in the system is designated by a lower case b (HAT-P-7b), and the next, with a lower case c (HAT-P-7c), and so on.

3) SEEDS (Strategic Exploration of Exoplanets and Disks with Subaru Telescope) is a large-scale, five-year strategic project led by Motohide Tamura (National Astronomical Observatory of Japan). Using a total of 120 observing nights at the Subaru Telescope, the project focuses on exploring hundreds of nearby stars in an effort to directly image extrasolar planets and protoplanetary/debris disks around stars.

4) Radial velocity is a measure of the rate of change in the distance of an astronomical object. When a planet orbits around a star, it causes a tiny shift in the star's spectrum which can be measured with a high-precision spectrograph and used to infer the presence of a planet.


Story Source:

The above story is based on materials provided by National Astronomical Observatory of Japan. Note: Materials may be edited for content and length.


Cite This Page:

National Astronomical Observatory of Japan. "Origin and maintenance of a retrograde exoplanet." ScienceDaily. ScienceDaily, 25 January 2013. <www.sciencedaily.com/releases/2013/01/130125103923.htm>.
National Astronomical Observatory of Japan. (2013, January 25). Origin and maintenance of a retrograde exoplanet. ScienceDaily. Retrieved October 26, 2014 from www.sciencedaily.com/releases/2013/01/130125103923.htm
National Astronomical Observatory of Japan. "Origin and maintenance of a retrograde exoplanet." ScienceDaily. www.sciencedaily.com/releases/2013/01/130125103923.htm (accessed October 26, 2014).

Share This



More Space & Time News

Sunday, October 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: China Launches Moon Orbiter

Raw: China Launches Moon Orbiter

AP (Oct. 24, 2014) China launched an experimental spacecraft Friday to fly around the moon and back to Earth in preparation for the country's first unmanned return trip to the lunar surface. (Oct. 24) Video provided by AP
Powered by NewsLook.com
China Prepares Unmanned Mission To Lunar Orbit

China Prepares Unmanned Mission To Lunar Orbit

Newsy (Oct. 23, 2014) The mission is China's next step toward automated sample-return missions and eventual manned missions to the moon. Video provided by Newsy
Powered by NewsLook.com
Russian Cosmonauts Kick Off Final Spacewalk of 2014

Russian Cosmonauts Kick Off Final Spacewalk of 2014

Reuters - US Online Video (Oct. 22, 2014) Russian cosmonauts Maxim Suraev and Alexander Samokutyaev step outside the International Space Station to perform work on the exterior of the station's Russian module. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
Comet Siding Spring Grazes Mars' Atmosphere

Comet Siding Spring Grazes Mars' Atmosphere

Newsy (Oct. 19, 2014) A comet from the farthest reaches of the solar system passed extremely close to Mars this weekend, giving astronomers a rare opportunity to study it. 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:

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