BBC News: Star system discovered

CNN: Dust ring around star looks like another solar system

Joint Astronomy Center

Wednesday 8th July, 1998

Astronomers discover a nearby star system just like our own Solar System

HILO, HAWAII -- An international team of astronomers from the Joint Astronomy Centre (JAC) in Hawaii, the University of California at Los Angeles (UCLA) and the Royal Observatory in Edinburgh announced today the discovery of a ring of dust particles around a nearby star, Epsilon Eridani, that appears to signify a Solar System very similar to our own.

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."

Why is Epsilon Eridani so interesting?

Greaves was a member of the international team that reported new images of dusty disks around the hotter stars Fomalhaut and Vega in April (Dusty Disks). However, the new image of Epsilon Eridani is even more exciting for several reasons:

"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.

More about the discovery:

Beyond Pluto in our Solar System is a region containing more than 70,000 large comets, and hundreds of millions of smaller ones, called the "Kuiper belt". The image obtained by Greaves' team shows dust particles that the astronomers believe are analogous to our Kuiper belt at the same distance from Epsilon Eridani as the Kuiper belt is from our Sun. Although the image cannot reveal comets directly, the dust that is revealed is believed to be debris from comets, Greaves said.

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.

How was the new image obtained?

The new image -- which is from short-radio wavelengths, and is not an optical picture -- was obtained using the 15-meter James Clerk Maxwell Telescope at the Mauna Kea Observatory in Hilo, Hawaii. The JCMT is the world's largest telescope dedicated to the study of light at "submillimeter" wavelengths. The team of astronomers used a revolutionary new camera called SCUBA (Submillimeter Common User Bolometer Array), which was built by the Royal Observatory in Edinburgh (which is now the UK Astronomical Technology Centre). SCUBA uses detectors cooled to a tenth of a degree above absolute zero (-273 degrees Celsius) to measure the tiny amounts of heat emission from small dust particles at a wavelength close to one-millimeter.

Implications and mysteries of the new discovery

What is the significance of the similarity between Epsilon Eridani and our own Solar System?

"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.

What is the bizarre bright spot in the image obtained by the astronomers?

"There may be a planet stirring up the dust in the ring and causing the bright spot," said Bill Dent of the Royal Observatory, Edinburgh, "or it could be the remnants of a massive collision between comets."

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

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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