Similar Solar System at 90 Light Years

A new planetary system has been discovered that is strikingly similar to our own. A planet with twice the mass of Jupiter orbits the star HD70642 at a distance of 3.3 AU, completing an orbit in 6 years. In comparison, Jupiter orbits our sun at 5 AU, completing an orbit every 12 years. In our solar system, 3.3 AU is roughly in the middle of the asteroid belt that fills much of the region between Mars and Jupiter.

Artist concept of star system, HD70642.
Credit:John Rowe animation

Just as the newly discovered plant is comparable to Jupiter in terms of mass and orbital distance, the star it orbits is a yellow dwarf similar to our sun. HD70642 is a 7th magnitude star, while our Sun has an absolute magnitude of 4.8.

The star HD70642 can be found in the constellation Puppis, but is not bright enough to be visible to the naked eye. HD70642 is about 90 light years away from Earth.

The planet orbits HD 70642 in a nearly circular orbit, similar to the circular orbits of the planets in our solar system.

Circular orbits may indicate a solar system’s suitability for life. Circular orbits ensure that a planet receives a consistent amount of sunlight, preventing seasonal extremes. Circular orbits also shouldn’t disrupt planetary systems, while elliptical orbits could gravitationally perturb orbits of other planets in a system, and perhaps even toss them out of the system entirely. Most extrasolar planets found to date have highly elliptical orbits.

Since the newly discovered planet is a gas giant similar to Jupiter, it probably does not harbor life. However, any moons orbiting this gaseous world could have the potential for life.

Astronomers already had found other Jupiter analogs, but this is the first time they have found a Jupiter analog in a solar system that so resembles our own. The solar systems of the other Jupiter analogs have Jupiter mass planets within the inner part of the systems – where, in our solar system, the terrestrial planets reside. The existence of a gas giant in the inner solar system would interfere with the formation of rocky planets like the Earth.

Since the inner solar system of HD 70642 seems to be free of Jupiter-mass planets, terrestrial worlds like the Earth could exist there.

Scene from a moon orbiting the extra-solar planet in orbit around the star HD70642. The planet has a mass about twice that of Jupiter and orbits the star in around six years, with a nearly circular orbit at more than three times the Earth-Sun distance. The star HD70642 is a 7th magnitude star in the southern constellation Puppis, and has properties very similar to that of our Sun.
Credit:David A. Hardy, (c)

A team of researchers from the Anglo-Australian Planet Search (AAPS) made the new planet discovery. They used the 3.9-metre Anglo-Australian Telescope [AAT] in New South Wales, Australia. Their research is supported by the National Science Foundation, the U.K. Particle Physics and Astronomy Research Council, and the Australian government.

AAPS team member Hugh Jones, of Liverpool John Moores University in the United Kingdom, announced the planet discovery at the conference "Extra-solar Planets: Today and Tomorrow" held in Paris, France. The team will publish their findings in an upcoming issue of Astrophysical Journal Letters.

The planet was found using the radial velocity technique. This technique looks at how stars are affected by the gravity of an orbiting planet. Over the course of an orbit, the planet will pull at the star from different sides. As a star moves away from us, the starlight is Doppler-stretched to longer red wavelengths. When the star moves toward us, the starlight is scrunched toward shorter blue wavelengths. Astronomers look at this light shift to determine characteristics of the orbiting planet.

Before the first extra-solar planets were discovered, researchers assumed that most solar systems would be similar to ours. Yet the majority of the more than 100 planet discoveries have elliptical rather than circular orbits. The planets also orbit either extremely close or very far from their host star.

When they first began looking for planets, planet hunters using the radial velocity technique were limited to searching for orbits that lasted a few days. As the time spent looking lengthened, orbital periods were found that lasted weeks, months, and then years. Now, after over 10 years of watching, planets with decades-long orbital periods are beginning to be found. Many of these later discoveries have nearly circular orbits.

What’s Next

The long-term goal of the AAPS team is to detect true analogues to our solar system: giant planets in long circular orbits and small rocky planets on shorter circular orbits. If such systems are found, astronomers will be able to determine whether planetary systems like our own are common or rare in the galaxy.

While all the extrasolar planets discovered so far are gas giants like Jupiter and Saturn, American and European scientists hope to launch missions over the next few years to search for terrestrial planets. For example, the Kepler space telescope will search for Earth-like planets when it is launched in 2007. In 2009, NASA hopes to launch the Space Interferometry Mission, which will look for Earth-sized planets around 200 stars.

Related Web Pages

Star chart
Kepler mission
Space Interferometry mission
Anglo-Australian Planet Search

Marcy-Butler: The Discovery of Extrasolar Planets
QuickTime Movie: Journey to HD70642 [MPEG]