A star much older than the Sun but similar in mass has been found to have a planetary system unlike any we have yet seen: It has at least six gas giant planets, with two in the habitable zone. To the best of our knowledge, life can't exist on planets like these, as their solid core is so deep inside that atmospheric pressures are phenomenal. However, moons could be a different matter, and we've found yet another configuration in which planetary systems can exist.
HD 34445 is a G0 star, just 7 percent heavier than the Sun and slightly richer in metals. However, at almost twice the age (8.5 billion years), it is more evolved, emitting twice as much light and puffing up on route to becoming a red giant.
Such a familiar-looking star 150 light-years away, which is close on galactic scales, inevitably attracted the interest of planet hunters. Observations have been made for 18 years, enough time to detect the wobble caused by the orbit of planets further out than Jupiter in our own system. The discovery of one planet in 2010 inspired further interest, and now a different team have announced five more on arXiv.
The paper revealing the discoveries notes: “The HD 34445 planetary system... is fundamentally unlike either our own solar system... or the Kepler multiple-transiting systems.” Only Jupiter and Saturn have enough gravitational effect on the Sun as to produce wobbles of the size we see from HD34445's six planets. The systems Kepler has revealed are made up of planets far more closely packed around the star.
The first of HD 34445's planets to be discovered had an orbit lasting almost three years, marking a significant breakthrough in finding planets at distances approaching those of the gas giants in our own Solar System, rather than the “hot Jupiters” that dominated early discoveries.
The new discoveries include planets with orbits similar to Venus, Mars, and Mercury, as well as one closer in and another well past Jupiter's. There's a gap about where the Earth would be, but even if it contained a rocky planet, HD34445's extra light makes this region too hot to support liquid water.
All the planets found so far have masses at least as great as Neptune's and are therefore almost certainly gas giants. Whether these planets have moons large enough to hold onto an atmosphere is impossible to tell, but if they do, the moons of the two suitably located planets (known as HB34445b and f by order of discovery) would probably have liquid water at the surface. The orbits appear to be nearly circular, thus avoiding the problem of where planets (or their moons) are alternately boiled and frozen.
Although planetary scientists are excited about the possibility of Europa or Enceladus supporting life, this would have to be in oceans deep beneath their frozen surfaces, and therefore probably limited in its development opportunities.
Unfortunately, as HD34445 ages, it is getting brighter and the habitable zone migrates outward. If life did evolve when the star was more stable, it would have needed to planet-hop outwards to survive.
Most of the planets we find beyond the Solar System circle stars so distant that they can only be seen with large telescopes. However, even a pair of binoculars will reveal HD 34445b east of Betelgeuse if skies are dark enough.
[HT: Bad Astronomy]