The Future of Our Sun

A newly discovered solar twin star allows astronomers to refine the expected development path of our Sun. The time that remains until the Sun will become too hot for liquid water on Earth will be about 2 billion years, the researchers say.

The team of astronomers led by Jose Dias do Nascimento from the Universidade Federal do Rio Grande do Norte, Brazil found the farthest known solar twin in the Milky Way Galaxy -- CoRoT Sol 1, which has about the same mass and chemical composition as the Sun.

Spectra from the High Dispersion Spectrograph (HDS) on the Japanese Subaru Telescope in Hawai showed that CoRoT Sol 1 is about 6.7 billion years old while space-based data from the CoRoT (Convection, Rotation and planetary Transits) satellite indicated a rotation period of 29 +/- 5 days. This newly discovered, evolved solar twin allows astronomers to uncover the near future of our solar system's central star -- the Sun.

Since the Sun is the closest star to Earth, it has been extensively studied in a variety of ways. Despite considerable efforts by astronomers, it is not yet known how typical a star the Sun is. Except for the youngest stars, the true rotation of those similar to the Sun is unknown, and there are few studies of mature solar twins or of more evolved ones.

The mass (the amount of matter) and chemical composition of a star are the main characteristics that determine its evolution. Studying stars with the same mass and composition as the Sun, the so-called "solar twins," can give us more information about our own Sun; solar twins of various ages offer snapshots of the Sun's evolution at different phases.

The satellite CoRoT (Convection, Rotation and planetary Transits) has provided precise space-based data from which it is possible to determine the rotation periods of stars. A meticulous analysis of the data showed that one of the several observed solar twin candidates was truly a star with a mass and chemical composition similar to that of the Sun. The finding was even more precious, because the star is at a more evolved stage and can serve as an indicator of the future of the Sun.

Determining the age of a star is probably one of its most difficult aspects to ascertain, but high quality spectra shed light on stellar ages. CoRoT Sol 1 is about two billion years older than the Sun, but its rotation period is about the same as the Sun's. Subaru Telescope's HDS spectra of CoRoT Sol 1 show that its overall chemical composition is similar to that of the Sun, but its detailed abundance pattern shows some differences, like most nearby solar twins. For example, the abundance of lithium (Li), an element that decreases with age, is less than that of the Sun.

Team leader Dr. Jose Dias do Nascimento commented on the significance of CoRoT Sol 1's age for understanding the Sun's future: "In two billion years' time, about the solar twin's actual age, the Sun's radiation may increase and make the Earth's surface so hot that liquid water can no longer exist there in its natural state."

In contrast to other solar twins that are relatively bright, CoRoT Sol 1, which is located in the constellation Unicorn (Monoceros), is more than 200 times fainter than the brightest solar twin known. The team plans to use the Subaru Telescope to continue its research on how typical a star the Sun is; they intend to describe its rotation evolution by finding solar twins representing a broad range of stellar ages and then placing the Sun within this context.