Tonight, the New Horizons spacecraft will fly by a chunk of ancient ice and dirt nicknamed "Ultima Thule." 4.1 billion miles distant from us, this small world, estimated at perhaps 20 miles across, is the the furthest object ever visited and examined by human technology. We should have first pictures and other information about it by Wednesday, when NASA plans a press conference.
The accompanying image shows an artist's attempt to draw this minor member of the zone beyond Neptune we call the Kuiper Belt. Pluto is also a member of this belt, but with far better property and voting rights than little Ultima. Several observations from afar have suggested that Ultima is elongated (maybe even two chunks that might just barely touch) and reddish. Its orbit indicates that it may well be very ancient, one of the first building blocks from which our solar system (the planets and moons that accompany the Sun) was assembled more than 4 1/2 billion years ago.
Moving at 32,000 miles per hour, and with sunlight only 1/2 of one percent as bright as it is at Earth, New Horizon's cameras will be put to the test to take pictures. The power (from radioactive materials) available to power the spacecraft is now only 190 watts! We will get within 2200 miles of the Ultima, closer than we got to Pluto with the same spacecraft in 2015.
New Horizons can either point at its target or at Earth. So it will at first send very little information and spend most of its time as it whizzes by pointing at Ultima. When it has gone by, it will point back to Earth and take 20 months to send the encounter data back to Earth (it's transmission rate is slow, but steady, much like this Facebook page.)
By the way, the term Ultima Thule means "Beyond the Known World"; it was term used on medieval maps to mark parts of our planet that were not yet explored and thus were veiled in mystery. (It was a nickname suggested in a public naming contest run by the SETI Institute.)
Keep your fingers crossed that things go better 4 billion miles from Washington DC than they have gone at home!