NASA's comet-chasing Stardust spacecraft is gearing up for a Valentine's Day date with Comet Tempel-1. Previously visited by Deep Impact six years ago, the rendezvous will be the first to examine the changes to a comet after it has journeyed around the Sun.

Comets, which are the oldest, most primitive bodies in the Solar System, preserve the building blocks of the Sun, planets and even life on Earth. They are also thought to play a role in delivering water and organic material to the Earth and other planets, and so learning about their composition is a vital step towards understanding the formation of the Solar System itself.

In July 2005 the Deep Impact spacecraft sent an impactor headlong into Comet Tempel-1 to analyse the composition of the debris thrown out of the crater in order to study the internal make-up of the comet. So much material streamed out of the cavity that the formation of the crater itself was obscured. But one of the aims of the new mission, rebranded Stardust-NExT (New Exploration of Tempel), will seek to identify and examine the crater.

Stardust first made headlines in 2004 having successfully rendezvoused with comet Wild-2, collected samples from its coma and jettisoned them back to Earth for analysis, which arrived safely two years later. Since then, it has been journeying towards Tempel-1 to make vital follow-up observations. The mission will be the first of its kind to revisit a comet, and the separation of six years, during which time Tempel-1 has looped around the Sun, will allow scientists to look at the changes that occur on a comet's surface after this high activity phase of a comet's orbit that sees an increase in outburst activity, its icy components evaporating and trapping dust grains which form a coma of material around its ice-rock core, or nucleus.

Tempel-1's orbit takes it as close to the Sun as Mars is, and almost to the distance of Jupiter. When Stardust-NExT makes its encounter it will be over 335 million kilometres away from Earth, and will swoop past the 6 kilometre-wide comet at a distance of 200 kilometres. Snapping 72 high resolution images it will follow up on the study of interesting features already observed on the comet's surface, such as smooth flow regions and active zones. The activity of the comet will also be monitored as the spacecraft approaches its target.

Although not the first spacecraft to visit two comets – in November last year the Deep Impact spacecraft flew by comet Hartley 2 (read more about that here) – Stardust-NExT will be the first spacecraft to compare the properties of two different comets using the same instruments, which will allow the most accurate data comparison yet.

“You could say our spacecraft is a seasoned veteran of cometary campaigns,” says Tim Larson, project manager for Stardust-NExT. “It’s been half-way to Jupiter, executed picture-perfect flybys of an asteroid and a comet, collected cometary material for return to Earth, then headed back out into the void again, where we asked it to go head-to-head with a second comet nucleus.”

The spacecraft is currently scheduled to make its date with the comet at 11:37pm EST on 14 February. The first images are expected to be available from approximately 4:30am EST on 15 February.