UPDATE: In a new release released today, NASA announced that it had finally decided not to make any plans to send the Dawn spacecraft to visit an additional asteroid. Apparently whoever posted yesterday’s Dawn diary was unaware of this decision. “The long-term monitoring of Ceres, especially as it moves closer to perihelion — the part of its orbit closest to the sun — has the potential to make more significant scientific discoveries than a flyby of Adeona,” said NASA director of science. Planetary Science Jim Green.
The announcement comes with good news for fans of the unknown: New Horizons has been cleared to visit a Kuiper belt object known as 2014 MU69. That rendezvous will take place in 2019. Given the unexpected nature of Pluto, a visit to a second body in the Kuiper Belt will provide much-needed perspective on these worlds.
Thursday marked the official end of NASA’s Dawn spacecraft primary mission. Dawn demonstrated the potential of ion engines in solar system exploration as it was able to encounter and enter orbit on two different asteroids, Vesta and Ceres. Scientifically, its findings have changed what we thought we knew about some bodies of the asteroid belt.
Dawn isn’t going to stop now that his mission is over, as he’s in reasonable shape and still observing Ceres. But there’s a hint that NASA has bigger plans for the spacecraft.
Yesterday, the Jet Propulsion Lab (which serves Dawn) posted and removed what it calls a “Dawn Journal” article. The entry described the future plans for Dawn, and it doesn’t involve staying in orbit around Ceres. Instead, the craft’s ion engines will be used to gradually push it away from Ceres. The energy-efficient, high-efficiency engines will take until the end of the year to free the spacecraft from the dwarf planet’s gravity.
Back in orbit around the sun, the craft will be on its way to a rendezvous in 2019 yet another asteroid, this one is called 145 Adeona. Discovered in 1875, this asteroid is quite large with a diameter of 150 km, but is much more typical of the bodies in the asteroid belt than Ceres or Vesta. Plans for the approach would allow for a relatively slow passage at 4,700 km/h – one-tenth the speed of New Horizons’ Pluto flyby.
Dawn has failed two reaction wheels, meaning it burns some of its maneuvering fuel (hydrazine) to stay oriented to communicate with Earth. Going back to deep space should allow the craft to minimize fuel consumption, extending its lifespan much longer than would be possible if it remained parked near Ceres.
Presumably, NASA will re-announce this plan sometime in the next few days once formal approval is given.