One of the nearest, reasonably Sunlike stars, with about three-quarters
the mass of the Sun and one-third the luminosity; it lies in the constellation
Eridanus at a distance of just over 10 light-years.
An orange-red dwarf, Epsilon Eridani spins relatively fast, with a rotational
period of 11 days (compared with the Sun's 27 days). This quick rotation
generates a comparatively strong magnetic field, which results in a lot
of chromospheric activity, including large starspots, and a variable spectrum
characteristic of a BY Draconis star.
Epsilon Eridani has been the target of intense scrutiny by SETI
projects, including the first, Project Ozma.
It is now clear why these searches could not have been successful: Epsilon
Eridani is a young star, with an age between 500 million and 1 billion years.
Intelligence could not have developed in so short a time, even given the
availability of a suitable planet. In September 1998, however, came news
that the Epsilon Eri system may be like the solar system in other ways.
Observations at submillimeter (very short radio) wavelengths showed that
it is surrounded by a ring of dust at about the same distance as that of
the Kuiper Belt from the Sun.1
A bright region in the ring might be caused by particles trapped around
a young planet, while a partially evacuated region nearer the star might
indicate the presence of other unseen worlds.
The density of dust in the Eridanian system is about 1,000 times that found
in the solar system today, but roughly what it would have been like in the
solar system about 4 billion years ago – about 600 million years after
the Earth and other planets formed, toward the end of the period of heavy
bombardment. This discovery adds to the growing body of evidence that planetary
systems around other stars are the rule rather than the exception. Moreover,
Epsilon Eri provides a window into what conditions may have been like in
the neighborhood of the Sun at a time when life was first beginning to emerge
on the young Earth.
| A 1998 image of the dust disk surrounding
In 2000, astronomers announced the discovery (or a possible confirmation
of earlier detections) of a Jupiter-like
planet around Epsilon Eri (see Archived News item below).2 In
October 2002 came news of a second planet in the Epsilon Eri system based
on morphological studies of the dust disk.3 One of the lowest
mass extrasolar worlds yet discovered, with a mass roughly one tenth that
of Jupiter, it also has by far the longest, largest orbit of any yet found
with an orbital period of 280 years. The presence of Epsilon Eridani C was
disclosed by researchers at the University of Rochester using a new technique
that does not use direct light from the star, but rather light radiating
from the dust surrounding it. Not all stars have large concentrations of
dust, but those that do, like Epsilon Eridani, can display telltale patterns
in their dust fields that may lead to planetary detection.
||10.50 light-years (3.22 parsecs)
||R.A. 03h 32m 56s, Dec. -09° 27' 30"
|mass (Jupiter = 1)
|semimajor axis (AU)
|orbital period (days)
- Greaves, J., Holland, W., Moriarty-Schiven, G., Dent, W., Zuckerman,
B., McCarthy, C., Webb, R., Butner, H., Gear, W., and Walker, H. "A
Dust Ring Around Epsilon Eridani: Analogue to the Young Solar System,"
Astrophysical Journal Letters, 506, L133 (1998).
- Hatzes, A., Cochran W., McArthur B., Baliunas S., Walker G., Campbell
B., Irwin A., Yang S., Kuerster M., Endl M., Els S., Butler P., and
MARCY, G., "Evidence for a Long-period Planet Orbiting Epsilon Eridani,"
ApJ. Letters, 544, L145 2000.
- Quillen, A., and Thorndike, S. "Structure in the Epsilon Eridani dusty
disk caused by mean motion resonances with a 0.3 eccentricity planet
at periastron," ApJ. Letters, 578, L149, 2002.
PLANETS AND SUBSTELLAR OBJECTS