In a terse statement, Dr. Mayor’s main rivals, a group of planet hunters led by Geoff Marcy of the University of California, Berkeley, and Paul Butler of the Carnegie Institution of Washington, said they were doing their own survey, to be completed within a year.

“Our survey will check the Swiss report that 30 percent of stars have super-Earths or Neptunes orbiting closer than Mercury does the Sun,” the group said in an e-mail message.

Dr. Mayor and his team discovered the first so-called exoplanet orbiting a regular star, known as Pegasi 51, in 1995. That planet, about half the mass of Jupiter, circles its star tightly in a four-day orbit. In the years since, some 270 exoplanets have been discovered, many of them like the original, so-called hot Jupiters in lethal scorching embraces of their stars.

Part of the reason that such unusual systems have been found first is that the detection method is biased toward finding large planets close to their stars. Both Dr. Mayor’s and Dr. Marcy’s groups use what is called the wobble method, deducing the presence of a planet by the to-and-fro gravitational tug it gives its star as it orbits. The more massive the planet and the closer it is, the bigger and more noticeable tug it will impart.

The tug perturbs the star’s velocity relative to Earth by as little as a few meters per second in the case of a super-Earth. That shows up as a periodic shift in the wavelength of light from the star.

In recent years, Dr. Mayor’s group has used a special spectrograph known as Harps, for High Accuracy Radial Velocity Planet Searcher, on a telescope at the European Southern Observatory’s site at La Silla, Chile, to detect such small wobbles in stars.

“Detection of planets with masses of about 2 Earth-masses (maybe less!) is possible,” Dr. Mayor said in an e-mail message.