Planet Orbiting Another Star Doesn’t Exist After All

Mount Wilson’s 100-Inch Telescope has played a crucial role in proving
that a previously announced “planet” orbiting a nearby star is only an
illusion.

MOUNT WILSON, Calif., October 16, 2002 To date, astronomers have
announced their “discovery” of more than 100 planets orbiting nearby
stars. But do all these planets really exist?

Not always, according to studies performed at Mount Wilson
Observatory’s 100-inch telescope and announced in the October 1 issue of
the Astrophysical Journal.

A research team consisting of Gregory W. Henry of Tennessee State
University and Sallie L. Baliunas and Robert A. Donahue of the
Harvard-Smithsonian Center for Astrophysics has shown that a “planet”
orbiting the star HD 192263, which had been announced by California and
Swiss researchers in 1999, actually does not exist.

The reason why this planet could be illusory is that in all these
“discoveries” you never actually see the planet. The evidence for it is
indirect; you detect a rhythmic shift in the parent star’s spectrum
from blue to red and back again, as the star moves toward and away from
us in response to the pull of the orbiting planet’s gravitational
force. But for stars like the Sun, with large “starspots,” the same
rhythmic spectral shifts can also be caused by the star’s rotation.
When a large spot moves across the star’s face as the star rotates, it
also causes a rhythmic shift in the star’s spectrum from red to blue
and back again, mimicking the rhythmic shift in the spectrum that would
be caused by a planet’s gravitational pull, without any planet being
present. Thus the planet searcher may believe he or she has found a
planet when actually none exists.

Baliunas, who serves as Deputy Director of the Mount Wilson Institute,
explained that data on sunspot-like activity cycles of HD 192263,
gathered at Mount Wilson as part of a long-term program to observe
sunspot-like activity on distant stars, were one of the key factors in
proving that the rhythmic changes observed in this star’s spectrum
were indeed caused by the star’s rotation and not by an orbiting
planet.

This is not the first time Mount Wilson’s starspot data has been used
to disprove an extrasolar planet’s existence. In 1998, Baliunas’ team
showed that the evidence for a supposed planet around the star HD
166435 was really produced by the star’s rotation, and the planet did
not exist.

The observing program at Mount Wilson Observatory that obtained the
starspot data for HD 192263 (called the “HK Project” because it measures
the intensity variations in the calcium H and K lines in the stellar
spectrum) was inaugurated by Mount Wilson astronomer Olin C. Wilson in
1966. It has monitored the starspot activity cycles of more than 100
Sun-like stars continuously for more than 34 years. This makes the HK
Project one of the longest-running continuous observational programs in
the history of astronomy.

Source: Mount Wilson Observatory