CNN: Dust ring around star looks like another solar system
Joint Astronomy Center
Wednesday 8th July, 1998
The ring is "strikingly similar" to the outer comet zone in our Solar System, and shows an intriguing bright region that may be particles trapped around a young planet, said JAC astronomer Jane Greaves, who led the research team.
"What we see looks just like the comet belt on the outskirts of our Solar System, only younger," said Greaves, who presented the findings today at the "Protostars and Planets" Conference in Santa Barbara. "It's the first time we've seen anything like this around a star similar to our Sun. In addition, we were amazed to see a bright spot in the ring, which may be dust trapped in orbit around a planet."
"Epsilon Eridani is far more similar to our Sun than either Vega Fomalhaut." she said. "This star system is a strong candidate for planets, but if there are planets, it's unlikely there could be life yet. When the Earth was this young, it was still being very heavily bombarded by comets and other debris."
"It is also a star in our local neighbourhood, being only about 10 light years away, which is why we can see so much detail in the new image"
Epsilon Eridani is clearly visible to the naked eye, in the constellation Eridanus (the River), which stretches from the foot of Orion (near the bright star Rigel) to the 9th brightest star in the sky, the southerly Achernar (barely visible from the USA and Europe). Epsilon Eridani is among the 10 closest star systems to the Earth.
"If an astronomer could have seen what our Solar System looked like four billion years ago, it would have been very much as Epsilon Eridani looks today," said Benjamin Zuckerman, UCLA professor of physics and astronomy. "This is a star system very like our own, and the first time anyone has found something that truly resembles our Solar System; it's one thing to suspect that it exists, but another to actually see it, and this is the first observational evidence."
The research team -- which also includes astronomers from the University of Arizona, University College London, and the Rutherford Appleton Laboratory -- has submitted its findings to the Astrophysical Journal Letters, the most widely-read scholarly journal in astronomy.
Epsilon Eridani's inner region contains about 1,000 times more dust than our Solar System's inner region, which may mean it has about 1,000 times more comets, the astronomers said. Epsilon Eridani is believed to be only 500 million years to 1 billion years old; our Sun is estimated to be 4.5 billion years old, and its inner region is believed to have looked very similar at that age.
In our Solar System, the first 600 million years was a time of "heavy bombardment" when the planets were assaulted by massive meteorites and other celestial objects until the gravitation of Jupiter and Saturn cleaned out these destructive objects. Life on Earth probably did not start until after the era of heavy bombardment, said JAC astronomer Wayne Holland.
"The implication is that if there is one system similar to ours at such a close star, presumably there are many others," Zuckerman said. "In the search for life elsewhere in the universe, we have never known where to look before. Now, we are closing in on the right candidates in the search for life."
Epsilon Eridani is probably too young to support even primitive life, the astronomers said, but there may be other similar star systems that are billions of years older, and are good candidates to search for life. Although astronomers have not yet located a star system that is the right age with the right atmosphere to support life, they are getting closer.
A region near the star that is partially evacuated indicates that planets may have formed, the astronomers said; the presence of planets is the most likely explanation for the absence of dust in this region because planets absorb the dust when they form.
Epsilon Eridani is about three-quarters as massive as the sun, but only one-third as luminous. When astronomer Frank Drake conducted the first serious search for radio signals from other civilizations in the late 1950s, Epsilon Eridani was one of the first two stars he studied. Today, researchers know something Drake did not: Epsilon Eridani is much too young to have intelligent life. However, the new image shows there may be at least one planet, and perhaps life in the future.
In addition to Greaves, Holland, Zuckerman and Dent, the astronomers on the project are Gerald Moriarty-Schieven and Tim Jenness at JAC; Harold Butner at the University of Arizona, Tucson; Walter Gear at University College London; Helen Walker at the Rutherford Appleton Laboratory; and UCLA graduate students Richard Webb and Chris McCarthy.
Information and images are available on the World Wide Web at website www.jach.hawaii.edu/News/kbelt.html
The JCMT is operated by the Joint Astronomy Centre, on behalf of the UK Particle Physics and Astronomy Research Council, the Netherlands Organisation for Scientific Research, and the National Research Council of Canada. This work was also supported, in part, by NSF and NASA grants to UCLA.
The submillimetre image of Epsilon Eridani, and how the Solar System would look if seen from the same distance
The left image is a false-colour view of a ring of dust particles around Epsilon Eridani, taken with the SCUBA camera at the JCMT.
The right image is a sketch of how the Solar System would look (in optical light) to an astronomer looking from Eps Eri, drawn to the same scale.
The submillimetre image shows the emission from dust particles, each a fraction of a millimetre in size, orbiting around the star Epsilon Eridani. The false-colour scale shows where the brightest regions are (yellow/red), in contrast to the areas with very little dust (blue/black). The dust lies mainly in a ring around the star, with a radius of 60 Astronomical Units (60 times the size of the Earth's orbit). The star itself was not seen, because its small, hot surface radiates very little at submillimetre wavelengths.
On the outskirts of the Solar System, there are vast numbers of comets beyond the orbit of Pluto (40 Astronomical Units). These make up the "Kuiper Belt". The sketch shows only a fraction of these comets, and they are not to scale. The giant planets -- Jupiter, Saturn, Uranus and Neptune (also not to scale) -- orbit inside this belt.
The location of the "belt" is remarkably similar in each picture. Epsilon Eridani is much younger than the Sun, only about 0.5-1 billion years old while the Sun is 4.5 billion years old. It is likely that that tiny dust particles around Eps Eri will gradually accumulate into comets like those in the Solar System's Kuiper Belt.
There is one prominent bright peak in the ring around Eps Eri, seen to the lower left of the star. This could be dust particles trapped in an orbit close to a planet, or (less likely) the remnants of a major comet collision. No-one yet knows if Epsilon Eridani has planets ... but the new image gives a clue that there may be.
In fact, a very similar picture has emerged of dust orbiting near the Earth. Dermott and co-workers made a simulation of dust trapped in orbits near the Earth, and their computer simulation can be seen here. It was published in 1994, in the scientific journal Nature. There is a striking similarity between their model for the Earth and our actual image of Epsilon Eridani!
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