Earth time July 14, 2015 at 11:50 UTC: On this date a new frontier will be reached as mankind will explore a strange new world, boldly going where no Man has gone before.
The explorer in question, not a person, but the robotic space probe New Horizons and the new world is within our solar system, the elusive celestial object known as Pluto.
Pluto inhabits the melancholic distances of the outer regions of our solar system, which has made its observation so difficult. Until now!
A bit more detail below.
Part 1 – The Visitor:
New Horizons is part of NASA’s New Frontiers space exploration program. It was built with the purpose to visit Pluto and whatever other TNO it might find in its path afterwards. It’s the very first mission to visit Pluto done my mankind.
New Horizons goals are to map the surface and characterize the geological, morphology and temperatures of Pluto and its moon Charon, characterize Pluto’s atmosphere, search for Charon’s atmosphere, search for additional satellites of Pluto besides the already known and conduct similar observations on other Kuiper Belt objects.
New Horizons was launched from Cape Canaveral on January 19, 2006. It is the fastest spacecraft ever build yet, breaking records since launch.
On February 28, 2007 it received a gravitational assist from Jupiter which helped gain even more speed, shortening its travel time by three years. While vising Jupiter it did some exploring of Jupiter and its moon Calisto, taking the best image resolution photographies of the planet yet. Then it went on hibernation mode for the remainder of the voyage to save on energy and components.
The craft is no larger than a grand piano, with a triangular shape, mostly made of aluminium and titanium. It’s powered by a Radioisotope Thermoelectric Generator (the sucker is nuclear!).
Its initial on-orbit mass was 470 kilogram, less than half the weight of a regular family sedan automobile.
Alas, New Horizons will not be put into Pluto’s orbit but it will just fly-by. It’s not a visit to stay. After that it will leave the Plutonian system and keep traveling the trans-Neptunian distances in search of other worlds.
New Horizons has Twitter pages at:
Part 2 – The Host:
Pluto is named after the Roman God of the Underworld.
Once known as a planet, since 2006 it was re-classified as a dwarf planet. There used to be no official definition for what is a planet. The discovery of Eris, another object situated beyond Neptune’s orbit and larger than Pluto prompted a definitive definition:
- Is neither a planet nor a natural satellite;
- Is in direct orbit of the Sun;
- Is massive enough for its shape to be in hydrostatic equilibrium under its own gravity;
- Has cleared the neighborhood around its orbit.
Pluto failed to fulfill the last criteria, as it is a member of the Kuiper Belt family of orbitals. As such a new definition emerged, Dwarf Planet, which today classifies Pluto.
As a consequence, this reclassification though it prompted the “demotion” of Pluto, it also caused the “promotion” of Ceres, once known as an asteroid, to dwarf planet as well. Ceres is itself another fascinating object which recent observations from has revealed to be a very dynamic world which might even harbor the conditions for life. And Pluto might also be one too. More of that later.
Another thing needs to be taken into account for the change of Pluto from planet to dwarf planet: Pluto is quite small. To give you an idea, it has about 18% of the mass of the Moon! While planet Mercury itself is smaller in volume to the Moon as well, in mass it’s 5 times heavier, to the point its gravity is almost similar to Mars. Pluto’s gravity is less than half the Moon’s!
Pluto is not itself an isolated planet but the main body of a planetary system. It has five moons called Charon, Styx, Nix, Kerberos, and Hydra.
Charon at half of Pluto’s diameter and 1/10th of its mass, it dominates the Plutonian’s Moon system.
Pluto and Charon tidally locked and orbiting a barycenter that exists outside the body of Pluto, unlike the Earth-Moon where the barycenter exists within the body of Earth.
Pluto and Charon both orbiting around a common point makes some call them a bi-planetary system, but it has not stuck yet as a definitive classification.
The other moons are very small, the largest a boulder a mere over 150 kilometers wide, to cause much of an effect on the rest of the system.
One curious aspect of the Pluto’s moons is they make for a very compact system and largely empty, all existing within only 3% of the region of Pluto’s inner Hill Sphere, the stable gravitational zone of a planet’s influence, whereas Moons could orbit Pluto at up to 53%. This has made some to think Pluto might have up to ten Moons orbiting it, with many yet undiscovered, which is one of the missions of New Horizons.
Pluto is probably mostly made of ice. Yet its surface color seems to be primarily orange or red, contrary to what might be expected (red ice?). Soon we will know better why.
The gravitational tug-of-war between Pluto and Charon might imply that they have a hot nucleus heated from gravitational tides. This has the implication that an internal ocean of liquid water might exist below the surface ice. If so, this also makes both Pluto and Charon candidates for harboring extraterrestrial life, just like how it might be for Jupiter’s moon Europa.
The discovery of Pluto is a story of a happy accident.
Planet Neptune was the first planet discovered by calculations based on irregularities on Uranus’ orbit, caused by a massive object orbiting further distant. Direct observation followed, with the planet discovered where it was first calculated to be.
Neptune was also observed to have irregularities in its orbit, so it was presumed that lie Uranus before, there must had been another large planet like Neptune itself further afield causing the disturbances. The race for the discovery was on!
None was more interested in the discovery of the new planet than Percival Lowell, a very enthusiastic and very wealthy astronomer.
Lowell dubbed it Planet X. But he didn’t lived to find it. His will left part of his considerable fortune to finance programs to search for it at the location he believed it to be found.
In 1929 the Lowell Observatory handed the job to then 23 years old Clyde Tombaugh. He was the perfect man for the job, for he was intelligent, resourceful, dedicated, and more importantly, he possessed a nearly inhuman patience. His job was to systematically photograph portions of the sky by night and by day he observed the plates looking for any moving object whose movement contrasted to the apparent fixed position of the stars.
Almost one year later, on 18 February 1930, Tombaugh discovered a new planet in the whereabouts to the position predicted by Lowell.
It was named from a suggestion made by then 11 years old Venetia Burney, who named it Pluto after the roman god of the underworld. The name stuck because it maintained the tradition of the naming of planets after the Roman pantheon and also because the first two letters of PLuto also make for the initials of Percival Lowell.
But soon enough things didn’t add up to Pluto being Planet X. Measurements of Pluto’s albedo revealed it couldn’t be larger than Earth, which made it already too small to be an object that could cause much influence on Neptune. Further observations revealed it to be progressively smaller than initially thought, and already a few decades after the discovery it was known that Pluto was even smaller than Mercury. Way too small!
Pluto was not Planet X.
More accurate observations and advancement in understanding orbital mechanics explained for Neptune’s supposed orbital irregularities and dispelled any necessity for the existence of Planet X.
So, Pluto was discovered by serendipity.
But there’s nothing serendipitous about New Horizons, however. The probe is deliberately sent to study Pluto. And on the 14th of July we will see it up close like never before. A new frontier in the solar system will be broken and mysteries revealed. And alike as it always happens on science new mysteries will emerge and a new frontier will be set further away. It is interesting times.
As always, thank you for reading. This is Asimovlives, signing off.