A while back I wrote a blurb on the Voyager probes, and how one of them took an awe-inspiring shot of our planet from the unfathomable distance of about four billion miles, give or take. Our whole planet, and everything we ever were or will be, everything we’ve ever done, everywhere we know, occupied less than a single pixel of the image. A dust mote suspended in a sunbeam, as Carl Sagan described it.
Transmitted at the speed of light, it took over five hours for the picture to get to us.
A show last night on one of the science channels reminded me of another, more recent mission. Roughly two decades after the Voyagers were launched, another probe named Cassini (after Giovnni Domenico Cassini, a 17th Century Italian astronomer who studied the moons and rings of Saturn) was sent to follow in some of the earlier probes’ footsteps. It was launched in 1997, and arrived at its final destination, Saturn, in mid-2004, having swung by Venus and Jupiter along the way. There it remained, studying the system of Saturn and its moons, and deploying a landing probe to the surface of Titan, the largest of the ringed planet’s satellites (the lander was named Huygens, after Christiaan Huygens, a 17th Century Dutch polymath who used a telescope of his own design to become the first to describe Saturn’s rings, discovering Titan in the process). Titan is a very large moon, just a little bigger than the planet Mercury, and has a thick atmosphere. Great oceans of liquid methane were found to cover large parts of its surface, leading exo-biologists to wonder whether methane might be used by living things in the same way terrestrial organisms use water – both are solvents for organic molecules, and biologically, methane-based life is quite plausible. NASA hopes to land a submarine on Titan to swim in its methane seas, and look for living things. Imagine – a submarine sent to wander the seas of an alien moon over three-quarters of a billion miles away. So far as we know, these are the only stable oceans apart from our own in the entire Solar System. We simply have to find out what’s in them.
Cassini soared among Saturn and its moons for the better part of a decade. Near the end, it was sent on several orbits through the gap between the planet and its great ring system, a daring move dubbed the “Grand Finale”. The odds were good that it might strike something and be destroyed (the “gap” wasn’t necessarily devoid of orbiting debris), but it dove into the danger zone 22 times without incident.
The scientific insights gained from the Cassini mission were numerous and exciting, but to those of us in the lay public, the best part was the multitude of gorgeous pictures that were taken – truly amazing pictures, many of which looked like special effects out of a high-budget science fiction movie:
Was anything ever more beautiful? What a privilege to live at a time when our robots can beam such pictures our way, across the vast gulf of space.
Other planets were often in the frame when images were captured, and Cassini, with better cameras than Voyager 1, and much closer to home, snapped several photos in which Earth is clearly visible off in the distance. In this one, we’re the bright little blueish object below the plane of the rings:
Even at about 1/5th the distance, we’re still little more than a pale blue dot.
Here’s a Cassini image of Earth and the Moon:
Cassini had on-board thrusters to allow it to change trajectory in its orbits. This made it possible to alter course and steer towards different objects that looked interesting to its controllers back in the Jet Propulsion Laboratory in Pasadena, but by 2015 it was running out of fuel. It was decided that the probe should be sent along an orbital path that would take it into Saturn’s atmosphere. Otherwise, beyond our control, it might eventually strike one of the moons, perhaps Titan or another where life might be present, and the scientists didn’t want to risk the contamination of alien ecosystems with terrestrial microbes that had hitched a ride on the probe (one supposes there was already a chance they’d done so with the Huygens lander, but I suspect it had been carefully sterilized). At the end of the Grand Finale, Cassini vanished beneath the clouds of Saturn and burned away.
If you’re keen, you can read about the Cassini mission here:
It was just a machine, and it was silly to get all emotional and teary-eyed at the thought of brave and plucky little Cassini plunging to its death. Everybody did, just the same.