When was gliese 581 found

Neither, he said, does another planet in the same solar system, known as Gliese d, announced in —less clearly hospitable to life, but still once seen by some astronomers as a possible place to find aliens.

The original evidence for both worlds' existence came from measurements of its home star, Gliese —a dim red dwarf, about a third as massive as the sun, that resides about 22 light-years away from our solar system.

Most exoplanets are too close to their stars to be seen directly with telescopes, so astronomers find them with indirect clues. In the case of Gliese g, they watched for subtle wobbles caused by the gravity of an orbiting planet tugging back and forth on the star in a regular pattern.

The time it took the "planet" to complete one orbit 37 days told them how far it was from the star. In the case of this cool star, that was "just at the right distance to have liquid water on its surface," Butler said at the time.

The strength of the tugging, meanwhile, told them the planet was about three times as massive as Earth. But even at the time, other astronomers questioned whether Gliese g was really there. A star's wobbles are measured by looking at its spectrum —its light, smeared out to form a sort of rainbow. The wobbles are so tiny, however, that it takes some statistical analysis to find a back-and-forth pattern.

Critics such as exoplanet expert Eric Ford , then at the University of Florida and now at Penn State, said that Butler's and Vogt's analysis was unconvincing, arguing that the pattern wasn't even clearly there. Robertson and his colleagues, however, did find a pattern: "There is a real, physical signal," he said.

The bad news: "It's just that it's coming from the star itself, not from the gravity of planets d and g. What's happening, they say, is that magnetic disturbances on Gliese 's surface—starspots—are altering the star's spectrum in such a way that it mimics the motion induced by a planet. The star itself rotates once every days, carrying the starspots with it; the disputed planets appeared to have periods of almost exactly one half and one fourth of the day period.

When the scientists corrected for the starspot signal, both planets disappeared. Butler declined to comment on the new result, and Vogt did not respond to an emailed request for comment. At the same time, subtracting the starspot signal actually made the evidence for three other worlds in the Gliese system—planets b, c, and e, all of which are too hot to be habitable—even stronger.

It's very encouraging, agreed Robertson, that "we can now take out the stellar influence and reveal the planet's existence. Animals Whales eat three times more than previously thought. Environment Planet Possible India bets its energy future on solar—in ways both small and big. Environment As the EU targets emissions cuts, this country has a coal problem. Paid Content How Hong Kong protects its sea sanctuaries.

History Magazine These 3,year-old giants watched over the cemeteries of Sardinia. Magazine How one image captures 21 hours of a volcanic eruption. Science Why it's so hard to treat pain in infants.

Science The controversial sale of 'Big John,' the world's largest Triceratops. Science Coronavirus Coverage How antivirals may change the course of the pandemic. Science Coronavirus Coverage U. Travel A road trip in Burgundy reveals far more than fine wine. Travel My Hometown In L. Travel The last artists crafting a Thai royal treasure.

Subscriber Exclusive Content. Why are people so dang obsessed with Mars? How viruses shape our world. The era of greyhound racing in the U. See how people have imagined life on Mars through history.

The region of habitability would likely be on the line between shadow and light. Gliese g was found by detecting the gravitational wobbles it induced in its parent star, but the researchers said it was subtle; more than observations were required at a precision of 1. Brightness measurements of the star were also confirmed with a Tennessee State University robotic telescope.

The planet's existence very quickly came under scrutiny. They saw signals for what they believed were four other planets in that system, but the information did not show Gliese g, they said. The paper was also published on preprint site Arxiv. This was a point that Vogt made in a Space.

He also said that his own team was unable to come to the same conclusions as the Swiss team — unless they removed a few data points. The research teams, each opposing the other, kicked off a flurry of publishing activity about g, sometimes also discussing the plausibility of other supposed planets in the system.

Among them:. Further study on g, however, cast strong doubts on its existence. In , a team led by Paul Robertson, a postdoctoral fellow at Penn State University, said that Gliese d another planet in the system is not visible in the data when making corrections for its sun's activity.

A press release by Penn State pointed out that sunspots could sometimes masquerade as planetary signals. The presence of Gliese g is inferred by looking at the orbit of Gliese d.