Step On The Scales: Weighing Up Planet Earth…

Scientists at the European Southern Observatory have identified the closest looking solar system to our own. They located a sun-like star more than 100 light years distant with as many as seven different planets, including one that might be the smallest ever found outside the solar system.

“We have found what is most likely the system with the most planets yet discovered,” says Christophe Lovis, lead author of the paper reporting the result. “This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”

Some of the planets identified are large but one is only 1.4 times the size of Earth. That’s getting tantalizingly close to finding what astronomers are calling the ‘Holy Grail’ of astronomy, locating a planet just like our own with a breathable atmosphere, moderate temperatures and orbital stability. Scientists have been spotting planets beyond our solar system for the past 15 years, and they’ve now cataloged some 450. They know there are many more out there. The newly found worlds are made essentially of rocks and ice with a solid core. The larger planets probably have a layer of hydrogen and helium gas like Uranus and Neptune and the sixth is possibly a Saturn-like planet.

“We also have good reasons to believe that two other planets are present,” says Lovis. One would be a Saturn-like planet (with a minimum mass of 65 Earth masses) orbiting in 2200 days. The other would be the least massive exoplanet ever discovered [2], with a mass of about 1.4 times that of the Earth. It is very close to its host star, at just 2 percent of the Earth–Sun distance. One “year” on this planet would last only 1.18 Earth-days.

“This object causes a wobble of its star of only about 3 km/hour — slower than walking speed — and this motion is very hard to measure,” says team member Damien Ségransan. If confirmed, this object would be another example of a hot rocky planet, similar to Corot-7b.

Since the Earth is suspended in space, it cannot be put on a scale and weighed to be compared to other planets. But scientists can estimate its total weight by, among other things, measuring its tug on orbiting satellites. We’ve used this method to weigh the Earth and it turns out to be a whopping 6.6 sextillion tons… that’s two 6s, followed by twenty zeros, or 6,600,000,000,000,000,000,000 tons! But Earth’s weight gain doesn’t stop there… it increases by 100,000 pounds each year from dust and meteoric material falling from the sky. How does this “weigh up” to planetary science?

“Clearly, the exploration of the low-mass planet population has now fully started,” says C. Lovis et al. “The HARPS search for southern extra-solar planets will become the main focus of the field in the coming years. It is expected that the characterization of planetary system architectures, taking into account all objects from gas giants to Earth-like planets, will greatly improve our understanding of their formation and evolution. It will also allow us to eventually put our Solar System into a broader context and determine how typical it is in the vastly diverse world of planetary systems. The characterization of a significant sample of low-mass objects, through their mean density and some basic atmospheric properties, is also at hand and will bring much desired insights into their composition and the physical processes at play during planet formation.”

Many thanks to Dave Reneke of Australasian Science Magazine for sharing and to Mission Green Globe and ESO for the images.