The storm-lashed worlds of Trappist-1

Red dwarfs are thought to be the most common types of star, but all are dim. Even the red dwarf and the nearest star to the Sun, Proxima Centauri at 4.2 light years, is some 70 times too faint to be naked-eye-visible under the darkest sky. It was reported last summer that Proxima had a planet slightly larger than the Earth which orbited within its habitable zone where liquid water might survive on its surface given an adequate atmosphere.

The news of another red dwarf, Trappist-1, broke in February. It boasts seven Earth-class planets, of which three lie in or close to its habitable zone. At 39 light years, it is a thousand times dimmer than Proxima but, whereas Proxima is never visible from Britain, Trappist-1 lies in Aquarius below the Square of Pegasus, albeit swamped by our predawn twilight in the E and near Venus at present.

The artist’s representation of the system shows planets ranging between 0.4 and 1.4 times the Earth’s mass, admittedly with rather large uncertainties. Their positions, not to scale, range from 1.6m km to 9.4m km from their star, all much closer than is Mercury to our Sun. Their orbital periods of between 1.5 and about 20 days are linked in precise ratios and mean that there are copious transits of the star, causing its light to dip and revealing their presence.

Observing how the star’s spectrum changes during these transits might tell us something about any atmospheres, and perhaps even life, but this will be a real challenge gives its faintness.

Now an analysis of data from the Kepler space telescope indicates that Trappist-1 is subject to frequent solar flares, blasting its planets with magnetic storms 100 to 10,000 times stronger than the most intense storms hitting the Earth. The implication is that these would disrupt any atmospheres and make the development of complex life unlikely.

Jupiter stood directly opposite the Sun in the sky on Friday and is close to tonight’s full moon. The pair pass some 30° high in the S as seen from Britain in the middle of the night, at 01:00 BST. Spica in Virgo lies 7° below-left of Jupiter.

Jupiter’s mass exceeds that of all the other planets, asteroids and comets combined but is barely one thousandth that of the Sun. It would have needed to be perhaps 15 times more massive for any form of nuclear fusion to spark in its core and for it to become a brown dwarf. Grow it another five-fold, however, and it would be a red dwarf star to rival Trappist-1, though whether we and the Earth would still be around is open to question.