Oops, TW Hydrae b Isn't a Planet; Just a Sunspot

By Nancy Atkinson - September 10, 2008 at 7:09 AM UTC | Exoplanets
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You gotta love this about science; someone is always checking your work. Early this year a new exoplanet discovery was announced: TW Hydrae b, a huge planet about ten times as massive as Jupiter. Astronomers thought the planet was in a super-tight orbit around its host star (TW Hydrae), circling in only 3.56 days at a distance of about 6 million kilometers, which is about 4 percent of the distance from the Sun to the Earth. However, another group of astronomers decided to analyze some new optical and infrared data to confirm the radial velocity signal of the planet. Something didn't seem right, so they ran a few more tests and computer models and determined what they were seeing wasn't a planet. It was a big sunspot. "Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54 deg can reproduce the reported RV variations," the astronomers reported in their paper. The rest of the astronomical world must agree with the new determination, as TW Hydrae b has now been dropped from the

Planet Quest New Worlds Atlas

(a fun site to peruse.) But nature doesn't like a void, -- and astronomers have been working hard in the planet-search department, -- so, three new extra solar planets have been discovered and added to the atlas, for a current planet count of 309.

GJ 832 b

is about half the

size

mass of Jupiter and orbits 3.4 AU from its tiny host star. The star is a yellow, sun-like G star, about 16 light years from Earth. It was found with the Anglo-Australian Telescope. Astronomers say it has the largest angular distance from its star among radial velocity detected exoplanets, which makes it a potentially interesting target for future direct detection.

HD 205739 b

was also just announced:. This exoplanet is 1.37 times the

size

mass of Jupiter, and orbits about .9 AU from its star, a blue to white star, which is 1.22x the size of the sun, and 294 light years from Earth. It has an eccentric orbit, and astronomers believe there may be an additional planet in this system, because of how the planet orbits.

Another planet found by the same astronomical team is

HD 154672 b.

This is a biggie, at about five times the

size

mass of Jupiter, but only about .6 AU distant from its star, which is just about sun-size, and about 213 light years from Earth. The planet has an orbital period of 163.9 days.

These last two planets were found using the N2K Doppler planet search program with the Magellan telescopes.

Sources: arXiv (

here,

here

and

here

) and Twitter,

PlanetQuest

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com