Tennessee State University astronomer Greg Henry said on Sept. 5 his team is very confident that signals thought to represent a planet's gravitational influence on the star's position -- a technique called radial velocity or the wobble method -- were instead dark regions, like sunspots, rotating across the star.

Swiss astronomer Stephane Udry, involved with one of two teams that independently detected the presumed planet around a star called HD 192263 back in 1999, was unavailable last week and only Monday responded to a SPACE.com query about Henry's research.

"We do not share at all the conclusions of Greg Henry," Udry said, citing new research by his Swiss team that has not yet been published. "For us the radial-velocity variation cannot be due to spots."

Science often works this way -- new measurements improve on previous understanding until the various efforts finally yield the truth and, often, improved techniques. Resolution probably won't come at least until other astronomers see the new Swiss data.

Last week, Henry said his team's new "photometric" measurements of star spots on HD 192263 reflect the same time period of repetition, 24 days, as the radial velocity measurements in 1999 made by Udry's group and a separate U.S. planet-hunting team. Henry thinks he's seen spots that reflect the rotation period of the star rather than the orbital period of a planet.

Star spots would move toward Earth on half of the portion of the star facing us and away from Earth on the other half. This would induce a Doppler shift -- exactly the effect planet-hunters look for in noticing a wobble in a star thought to be caused by the gravity of a planet.

Henry explained, however, that theorists don't know exactly how these spots influence radial velocity measurements.

And since Henry's measurements were taken many months later than the original 1999 discovery, he can't say whether the two repeating cycles are in synch. If they are not, then each measurement could have been generated by different phenomena -- probably two separate star spots and not a planet.

The new measurements by Udry's Swiss team are the first to make simultaneous radial velocity and photometry measurements of the star. The researchers have concluded "the radial-velocity variation is not coming from the photometric one," Udry said, and they still believe they have a planet candidate.

Henry has not seen the Swiss results and could not comment on their merit.

But in a telephone interview he said it will be valuable for astronomers to reach a conclusion, mostly because they will then likely gain a better understanding of the methods they use to hunt for planets and account for possible effects of spots.

"Either way it's resolved, it's no big deal," Henry said. "But it is interesting. We do certainly need to understand" the relationship between the planet signals and star spot data.

Henry points out that most of the 100 or so planets found around other stars are not in question. The stars they orbit are very old and not thought to have spots big enough to significantly affect radial velocity measurements.

More Exoplanet News | Astronotes