FAQ: Inside NASA's Valentine's Day Visit to Comet Tempel 1

On Valentine's Day (Feb. 14), NASA's Stardust-NExT spacecraft will make a close flyby of comet Tempel 1, zipping to within just 124 miles (200 kilometers) of the icy wanderer.

The mission will mark the second time a spacecraft has visited two different comets (Stardust's original mission was to the comet Wild 2) during its lifetime.  It's also the first time two different spacecraft have visited the same comet after years of spaceflight.

NASA's Deep Impact mission sent a spacecraft to rendezvous with comet Tempel 1 in 2005 to intentionally slam a probe into the icy object to look inside the comet. The Deep Impact spacecraft was later recycled to visit another comet – Hartley 2 – in 2010.

Here's a brief overview of the spacecraft and its mission.

Does Stardust-NExT have anything to do with NASA's old Stardust mission?

Yes — it's the same spacecraft with a different mission. NASA's Stardust probe launched back in February 1999, tasked with gathering bits of dust and gas from around comet Wild 2 (pronounced "Vilt 2") and sending the sample back to Earth in a return canister.

The original Stardust did its job. It flew by Wild 2 in January 2004, and the comet material it collected made it to Earth two years later. Since the probe was still in good shape and had a fair amount of fuel left, NASA gave it a new mission in 2007 — to meet up with comet Tempel 1 this year. 

Along with that new mission came a new name: Stardust-NExT (for "Next Exploration of Tempel").

Why Tempel 1? And what does the new mission hope to accomplish?

Another NASA mission, called Deep Impact, visited Tempel 1 back in 2005. But it did more than visit: Deep Impact slammed an impactor into Tempel 1's surface, then studied the ejected material to get an idea of what the comet is made of.

Researchers hope Stardust-NExT will give them an idea of how Tempel 1 has changed during this time. They also hope to get a good look at the crater Deep Impact created; the previous mission was not able to see it well, as the huge cloud of ejected debris obscured the new feature.

Another aim is to extend geologic mapping of Tempel 1's surface, adding to the work done by Deep Impact. Through making these and other observations, Stardust-NExT can contribute to scientists' understanding of how comets formed at the solar system's birth and how they have evolved since then, researchers have said.

How big is Comet Tempel 1?

Comet Tempel 1 is 3.7-mile-wide (6 kilometers). It completes an orbit every 5 1/2 years, so it has circled the sun once since Deep Impact's visit.

How will Stardust-NExT fly by the comet?

Stardust-NExT will make its closest approach to Tempel 1 around 11:40 p.m. EST on Feb. 14 (0440 GMT on Feb. 15). At that time, the probe — zooming through space at around 22,400 mph (36,000 kph) — will come within 124 miles (200 km) of the comet, snapping pictures and making measurements all the while.

The probe will take 72 high-resolution images during the flyby and begin transmitting them to Earth an hour after the closest pass. It will take about 12 hours for all the pictures to reach scientists on the ground, researchers have said.

This NASA video describes the Stardust-NExT probe's Valentine's Day encounter with Comet Tempel 1.

How was Comet Tempel 1 discovered?

Comet Tempel 1 was discovered onApril 3, 1867 by Ernst Wilhelm Leberecht Tempel of Marseilles, France. Because of its periodic nature, 19th-century astronomers kept a close watch on Tempel 1.

They observed its return to the inner solar system in 1873 and then again in 1879, but by 1881 gravitational interactions with other objects had changed its orbital period to 6 1/2 years. The comet was then "lost" to observers, according to NASA. Attempts to spot it in 1898 and 1905 failed.

In the 1960s, the late comet hunter Brian Marsden studied Tempel 1's disappearance and predicted it would return in 1967 and 1972. Indeed, the comet was returned on June 8, 1967, then again in January 1972.

Tempel 1 now has the official designation comet 9P/Tempel 1. Its orbit has settled into its current 5 1/2-year period and carries the comet between the orbits of Mars and Jupiter.

Is there another comet encounter in Stardust-NExT's future?

Not likely. The Stardust-NExT probe will burn up almost all of its remaining fuel chasing down Tempel 1, so this will almost certainly be its last comet encounter mission, researchers have said.

The probe has been a model of reliability and longevity, lasting 12 years in space and putting about 3.7 billion miles (6 billion km) on its odometer. So if all goes well on Feb. 14, Stardust-NExT can drift off into the cold depths of space with its head held high.

You can follow SPACE.com senior writer Mike Wall on Twitter: @michaeldwall.