WEEKLY WHINE

Earth treats the Solar System with dignity

There now follows a ranking of the top interplanetary probes that are currently active. Eligible probes include those that are in lunar orbit, heliocentric orbit, or beyond, and that are currently in regular contact with Earth.

1. Voyager 2: American spacecraft in the heliosheath. Has been active for more than thirty nine years, and flew by all four gas giant planets.
2. Voyager 1: American spacecraft in interstellar space. Has been active for more than thirty nine years, and was the first spacecraft to exit the heliosphere, the region of space dominated by the Sun’s influence.
3. Cassini: American spacecraft in Saturnian orbit. Has been active in Saturnian orbit for more than twelve years, and will start its descent later this month before a controlled crash into Saturn in September.
4. Akatsuki: Japanese spacecraft in Venusian orbit. Was originally intended to enter Venusian orbit in 2010, but its main thruster failed. It successfully entered Venusian orbit at the second go in 2015 using four attitude control thrusters.
5. Mars Exploration Rover-B: American spacecraft in the Meridiani Planum on the Martian surface. Has been active on the Martian surface for more than thirteen years and has travelled over forty kilometres so far.
6. Mars Express: European spacecraft in Martian orbit. Has been active in Martian orbit for more than thirteen years.
7. Mars Reconnaissance Orbiter: American spacecraft in Martian orbit. Has been active in Martian orbit for more than eleven years.
8. 2001 Mars Odyssey: American spacecraft in Martian orbit. Has been active in Martian orbit for more than fifteen years.
9. OSIRIS-REx: American spacecraft on its way to 101955 Benna. Will attempt to return a sample to Earth.
10. Hayabusa 2: Japanese spacecraft on its way to 162173 Ryugu. It carries a lander and an impactor, and will attempt to be Japan’s second successful asteroid sample return.
11. ARTEMIS: Pair of American spacecraft in lunar orbit. They were originally part of the THEMIS mission of five spacecraft orbiting Earth, but two of them were repurposed to observe the Moon’s interaction with the Sun’s magnetic field.
12. Mangalyaan: Indian spacecraft in Martian orbit. India’s first interplanetary probe, it has been active in Martian orbit for more than two years.
13. Juno: American spacecraft in Jovian orbit. The first mission to the outer Solar System to be powered entirely by solar arrays.
14. New Horizons: American spacecraft in the Kuiper belt. Was the first spacecraft to fly by 134340 Pluto, and will fly by 2014 MU₆₉ before exiting the Solar system.
15. Dawn: American spacecraft in orbit around 1 Ceres. Spent more than a year in orbit around 4 Vesta before continuing to 1 Ceres.
16. Mars Science Laboratory: American spacecraft in Gale Crater on the Martian surface. Has been active on the Martian surface for more than four years and has travelled over fifteen kilometres so far.
17. Lunar Reconnaissance Orbiter: American spacecraft in lunar orbit, mapping the Moon’s surface, resources, and radiation environment. Has been active in lunar orbit for more than seven years.
18. MAVEN: American spacecraft in Martian orbit. Primarily observes the Martian atmosphere.
19. Trace Gas Orbiter: European spacecraft in Martian orbit. Began aerobraking to a lower orbit last month, and will primarily observe trace gases in the Martian atmosphere.
20. Chang’e 2: Chinese spacecraft in heliocentric orbit. Spent about eight months in lunar orbit, then flew by 4179 Toutatis, and is now about 300,000,000 km from Earth.