about 1 atom per cubic centimeter

interstellar medium

Helix Nebula

Since hydrogen is the main constituent of interstellar gas, we often characterize a region of space according to whether its hydrogen is neutral or ionized.

hydrogen

Hot things move quickly, cold things very slowly. If atoms come to a complete stop, they are at absolute zero. Space is just above that, at an average temperature of 2.7 Kelvin (about minus 455 degrees Fahrenheit).

Voyager 1 is expected to keep its current suite of science instruments on through 2021. Engineers expect each spacecraft to continue operating at least one science instrument until around 2025.

In 56,000 years, Voyager 1 will exit the Oort cloud, then brush by the stars GJ 686 and GJ 678 in 570,000 years.

A 1977 painting of Voyager 2 travelling through our solar system on its investigative mission. While Pioneer 10 and 11 are now inactive, New Horizons and both Voyager spacecrafts remain operational, powered by radioisotope thermoelectric generators.

A third Voyager mission was planned, and then canceled. Apparently, Voyager 3 was cannibalized during construction: On the second chapter, it is listed that there were three Voyager spacecraft. The second Voyager, VGR 77-2 had flaws and it was used for spare parts for Voyager 1 (VGR 77-1) and Voyager 2 (VGR 77-3).

In August 2012, Voyager 1 made the historic entry into interstellar space, the region between stars, filled with material ejected by the death of nearby stars millions of years ago. Voyager 2 entered interstellar space on November 5, 2018 and scientists hope to learn more about this region.

Voyager 2, currently some 11.5 billion miles from Earth, is back online and resuming its mission to collect scientific data on the solar system and the interstellar space beyond. In a statement, NASA confirmed that Voyager 2 is back in business.

Voyager 2, which is traveling in a different direction from Voyager 1, crossed the heliopause into interstellar space on November 5, 2018. The Voyagers have enough electrical power and thruster fuel to keep its current suite of science instruments on until at least 2025.

(Voyager 2’s twin, Voyager 1, is able to communicate with the other two stations.) A round-trip communication with Voyager 2 takes about 35 hours — 17 hours and 35 minutes each way.

Since launch on Aug. 20, 1977, Voyager 2’s itinerary has taken the spacecraft to Jupiter in July 1979, Saturn in August 1981, and then Uranus. Both Voyager 2 and its twin, Voyager 1, will eventually leave our solar system and enter interstellar space.

NASA’s Voyager 2 is the only spacecraft to have visited Uranus and Neptune, in brief fly-bys in the 1980s.

The record for the farthest distance that humans have traveled goes to the all-American crew of famous Apollo 13 who were 400,171 kilometers (248,655 miles) away from Earth on April 14, 1970. This record has stood untouched for over 50 years!