EXCURSIONS

Jon visits a Neptunian world surrounded by an asteroid belt that dwarfs our own

There’s an understated star with the designation HD 69830 in the quirkily named constellation of Puppis. Although this orange-glowing, seven-billion-year-old star is too southerly to be seen from UK skies, it’s very much worth a trip because of an astonishing feature encircling it: the most colossal asteroid belt. Detected in 2005 by NASA’s infrared Spitzer Space Telescope, this asteroid belt is 20 times more massive than the one between Mars and Jupiter in our Solar System.

It’s the kind of environment envisioned by Atari back in 1981. To navigate safely to my destination I’ll have to steer the Perihelion ship with the skill of Han Solo.

Of the planets known to exist in this system, I’m heading for HD 69830 d, nestled in the habitable zone. This world takes 197 days to complete an orbit at a distance of 0.6 AU from its parent star. It’s a rather Neptunian planet, around 18 times the mass of Earth, and there doesn’t seem to be a solid enough surface on which to land. What’s more, the strength of gravity on this world would be sufficient to contort my facial expressions into a permanent state of Les Dawson. So I’m landing on an icy moon close by to give a steadier, terrestrial base to observe from.

The glow from star HD 69830 marinades all of the bodies in the system in a rich golden hue reminiscent of an Andalusian evening seen through bronze-coloured sunglasses. From the moon, HD 69830 d boldly appears top-half only, like an imposing curved mountain of emerald and earthshine blue. Its blend of blues and greens is midway between Neptune and Uranus, so ‘Uratune’ seems a fitting name for this resplendent planet.

Soon, as the alien sky deepens in darkness, the spectacular effects of the massive asteroid belt become breathtakingly visible. The volumes of residual dust created by a belt of this magnitude give rise to a zodiacal light around 1,000 times brighter than our version visible from Earth. Back home we see the ‘false dawn’ of the zodiacal light as a quietly beautiful, eerie glow veiled through the night sky like a cone-shaped ghost. From the surface of the Uratunian moon, this system’s zodiacal light is more like a searchlight beam .

It’s a staggering view of the giant asteroid belt. The first comparison that flashes to mind is a view of the Milky Way observed from the darkest Earthly deserts. But the visual texture of this asteroid belt is coarser and thicker, as though our Milky Way has been redrawn with chunky Ceefax graphics.

Viewed through the comet hunter binoculars I keep in the Perihelion’s glove box, shapes, features and texture on many individual asteroids can be made out. It’s amazing to behold the brightening bronze to gold shades of these jaggededged space rocks as they arc upwards into the alien night sky.

This magnificently robust asteroid belt, four other neighbouring moons, a zodiacal light of such luminosity you’d think it was close to igniting and the planet Uratune setting with silent authority: what a crowded and glorious alien night sky!