It’s another Friday, so another Sky Candy coming up. I promised I’d concentrate on planetary stuff this week, so of course the feeds have been full of galaxies and nebulae. But I promised more planetary stuff for this week, and planetary stuff you shall get.
I just want to warn you, this is a long one.
It’s interesting to think about how much our idea of the planets and satellites in our solar system have changed.
When Heinlein was writing the famous juveniles, we thought Mars had something like a breathable atmosphere — thin, but adequate for Tibetans and Altiplano Indians — and canals, and, for that matter, Martians. Basically Perceval Lowell’s Mars. Ganymede was a rocky moon, terraformable with the (essentially magic) “heat trap”. Venus was a jungle world, the clouds being a perpetual thunderstorm. Even that was a stretch; Bradbury’s endlessly raining swamp would have fit better.
But what is Venus really like? A hellish place, the hottest surface in the solar system, even hotter than sun-side Mercury. The Jovian moons are either ice-balls or Io. Speaking of hellish.
But what we lost in science fiction, we gained in wonder.
We'll start on Earth but look to the stars.
The Earth, Terra, our home, was so much more than the brown and blue globe in Geography class.
It wasn't as separate as we imagined.
Then we went to the Moon. THE Moon, not just any moon. And there it was.
We're almost used to it now, but we still can't resist new pictures.
And there was a whole new Moon to be seen from outside.
This is a very high-definition photo that Andrew McCarthy has shared with all.
On Mars, instead of Schiaparelli's Canali or Lowell's canals, we have canyons that dwarf the Grand Canyon...
... and a Mount Olympus suited to the gods.
Ray Bradbury wrote not to be disappointed that we didn't find Martians because we are the Martians. Only robots so far. So far.
Venus doesn't have jungles; it's a hellscape that would have daunted Dante. But it's locked in a resonance dance with the Earth.
The clouds make Venus a mystery that's only slowly being cracked.
And the surface melts robots, but we got a look anyway.
Mercury was sneaky. Until a few years ago, we thought it was tidally locked to the Sun — one side always burning, the other black.
it’s much more complicated than that. One Mercury solar day (one full day-night cycle) equals 176 Earth days – just over two years on Mercury. Just enough that until we had an orbiting mission, it coincidentally always showed the same site to us.
Even though it has warm (!!) days and even colder nights, it's hot enough that sodium evaporates from the surface, making it a planet with a tail.
Pluto. Ten years ago we knew almost nothing about Pluto. Fifty years ago, all we knew about Pluto was, well, it was Out There. A dot on a photographic plate. Anyway, Pluto was a planet then (I maintain it’s still a planet) but not a place, not somewhere. And certainly not somewhere with a big red heart painted on the surface.
Pluto is tiny, smaller even than Mercury.
Then the New Horizons mission got to Pluto.
Again, it turned from a dot into a place. With mountains and plains and a big red heart.
Saturn — we always knew Saturn was going to be spectacular; we could see the Rings — but it turned out to be so much more. From Earth, even with a really big telescope, the Rings look like a celestial dinner plate. Up close, they are a complicated collection of concentric rings, with shepherd moons braiding some of the rings. And there's Titan, the only place in the solar system outside Earth that has liquid seas and rivers on the surface — but the liquid is methane, natural gas, and the land is made of water ice.
Saturn's moons are worlds in themselves.
Then there are the asteroids. Ceres really is like a minor planet, with water geysers and salt volcanos. We know of one asteroid — Psyche — that is all metal, or nearly so, and many of the asteroids — the carbonaceous chondrites — are made of something that’s as much like tar as anything we have on Earth.
Jupiter. Hard to come up with sufficiently expansive words about Jupiter.
I think the best I can do is promise that there will be more pictures of Jupiter. How would you all feel about a whole Sky Candy of Jupiter and its satellites?
The biggest surprise about the solar system is how complicated it all is. Mars may not have canals — but it could have had them a billion years ago. We thought Venus would be a near-twin of Earth. Venus isn’t like Earth at all.
Mercury isn’t tidally locked to the Sun as we thought until a few years ago. It’s much more complicated than that, turning in its orbit three times in two “years,” and Venus turns backward very slowly.
And water is everywhere, or almost. Earth of course. Mars in the ice caps and buried. The Moon, on the poles — which is why there’s a low-key race to get humans to the South Pole. Even the poles of Mercury.
But Ceres. Europa. Enceladus.
Here’s a prediction, one that I probably won’t see tested: where there is liquid water, there is life.
To think I was worried that I would not have enough material.
