The Martian moon Phobos, as seen by the ISRO’s MOM and its Colour Camera. Courtesy ISRO.
It’s been a while since I’ve written about Mars, and in particular, the Mars Orbiter Mission circling the Red Planet under the control of scientists at the Indian Space Research Organisation. It’s imaging the planet and studying the atmosphere.
While everybody’s attention has been focused on Dawn and New Horizons and other missions, this spacecraft has been sending back image after image of the planet, taken with the Colour Camera. Like this one — a shot of the tiny moon Phobos silhouetted against the Martian surface. They don’t go into a lot of detail about each image, so I wonder if the blue line along the limb is the thin atmosphere?
This mission was launched as a test of flight hardware, a sort of “proof of concept” for the Indians to use as they plan further adventures in space. The images are really quite lovely, and the organization has put up a nice gallery here. It’ll keep you busy while waiting for future communications from MOM (and all the other missions at Mars); right now the planet is behind the Sun as seen from here on Earth. That makes it difficult to talk to spacecraft until July 1, 2015. To be safe, the spacecraft’s instruments have gone into hibernation, and will awaken when it’s safe to talk to Earth again.
Take some time to browse the MOM site and marvel at what the Indians have accomplished with their first planetary flight!
The Moons of Pluto, as interpreted by an artist. Shapes are determined by data analysis of light reflected from these moons and seen by Hubble Space Telescope. Courtesy NASA/ESA/STScI
Take two worlds in orbit around a common center of gravity and call them Pluto and Charon. Pluto’s the main one, Charon’s called a “moon”. Their motions around each other create a shifting gravitational field environment. Think of it like two tennis balls whirling around each other in a pond. If you are trying to navigate around them, you have to deal with the waves in the water.
In a similar way, anything ELSE in orbit in the Pluto system is going to be torqued around — literally — by the gravity fields interacting. That’s what’s happening with two of Pluto’s smaller worlds calle Nix and Hydra. They actually wobble quite chaotically in their orbits, and it’s quite likely that the other two moons — Kerberos and Styx — are also orbiting in a chaotic fashion.
These small, potato shaped moons are also tidally locked together, meaning that gravitational influences between them and their larger system buddies make it so if you could view the system from the surface of Nix, its sister moon Styx orbits twice for every three orbits made by Hydra, and so on. Nix, Styx, and Hydra are locked in a resonance, which means that there is a ration bwewteen their orbital periods.
So, the system isn’t completely chaotic. Nothing’s flying off into space, but they ARE tumbling wildly. The motions, as observed by the Hubble Space Telescope, are filling in details about this system and the motions of its members. This is a cool piece of information to get, now that we’re less than six weeks from the New Horizons mission to flyby of Pluto. The hits just keep on coming!
The big question now is: how did those moons get those wild orbits? The best hypothesis is that early in Pluto’s history, it collided with another dwarf-planet-like object. As usual with collisions, lots of debris was generated, and it went spinning into orbit. Gradually pieces coalesced, the resulting small moons fell into the orbits they occupy today. Of course, there are still some details to work out, but since collision and coalescence seem to be major themes in planetary formation, and not just in our own solar system, this seems to be the story that astronomers will follow up on.
One other cool thing about Hubble observations: it appears that the small moon Kerberos is dark — like charcoal. The others are much brighter, so why is this one so shady? Good question, and the answer will have to wait until New Horizons is there to take a direct “look” at the surface. Onboard instruments should uncover the chemical makeup of the surface.
