Ceres, Dawn and (no) Panspermia

Published 2009-03-06 by Chris

I’m pretty excited about the Dawn satellite, currently hurtling its way towards the asteroid belt, and more specifically the dwarf planets of 1-Ceres and 4-Vesta. 4-Vesta is the primary candidate for the parent body of the important Howardite-Eucrite-Diogenite (HED) family of meteorites. The flyby of Dawn and its onboard spectrometer in 2011 and 2012 will either lend weight to, or dispute the aforementioned parent-body claim. The flyby therefore has the potential to make the HED meteorites only the third set of extraterrestrial samples with a known parent body (the other two sets are the lunar samples and the Shergottites, Nakhlites and other Martian meteorites).

Another important part of the Dawn mission will be swinging passed 1 Ceres (Ceres for short), the largest body in the asteroid belt, but the smallest identified dwarf planet in the solar system. There’s strong evidence Ceres contains a lot of water. The implications of water on an extraterrestrial body need not be repeated here, I’ll assume you’ve jumped to the same hope that some in the astroblogosphere have: life! The source of the panspermia that seeded the Earth!

This brings me to one of my major annoyances with the subject of panspermia. Don’t get me wrong, I think the idea is fascinating, and the prospect of interplantary geographical isolation and it’s evolutionary prospects makes me giddy. But the mere prospect of Earth being seeded from a source within the solar system just seems plainly ridiculous, and frankly, verging on the fantastical. Let me explain.

The Murchinson meteorite is a carbonaceous chondrite which landed near the town of Murchison in Victoria, Australia on the of 28th of September 1969. Murchison and its associated CM-class of meteorites are incredibly important because in addition to the normal treasure trove of mineralogical gems (some of which are literally gems) you’d expect from a carbonaceous chondrite, Murchison contains something very unusual: amino acids. The particular amino acids are not a form of contamination from Earth – the living systems on Earth which produce amino acids have a heavy preference for “left-handed” molecules (see the article Meteorites Made Life Left Handed), while the acids from Murchison have a left-hand/right-hand ratio of ~55/45 t0 60/40 (and that slight difference may have pushed life here to be left handed, see the aforementioned article for details). It’s therefore reasonable to assume that no living system has gotten in there and biased the handedness of the molecules present (at least, that’s extremely unlikely).

Murchison, being a carbonaceous chondrite, is from a parent body (we’re not sure which), which was not big enough to melt and differentiate. This implies that the amino acids we find in Murchison were formed either in space, or in a very, very low gravity situation. Therefore, amino acids, the building blocks of DNA, could very well form in space, away from any biological systems, and then rain down on planets during the formation of a solar system. So the building blocks of DNA can form in space without life and rocks containing these chemicals are still raining down, to this very day on Earth.

Why then do we require a hypothesis that Earth was seeded by already-formed life from somewhere else? This is the exact same infinite-regress problem one arrives at when debating the existence of a god – if the creator created everything, who created the creator? What is wrong with the concept that life formed, originally, on Earth, from the basic ingredients? Earth had the conditions right – liquid water, and therefore a warm environment, a protective magnetic field, a thick atmosphere (but no too thick), also protective from the nasty radiation of space, and a good, steady, consistent orbit. Ceres too may have had similar conditions 4.55 billion years ago, and it too would have had amino acid-laden meteorites raining down on it prior to and during the late heavy bombardment. If you’re willing to accept that life formed on Ceres, Mars, Venus or any other body from the same raw ingredients the Earth was receiving, but that life  THEN had to be transported to Earth, why not cut out the middle-planet and concede that life probably formed on Earth?

The hunt for extraterrestrial life will continue, and will remain exciting. Should I be privileged enough to see its discovery in my lifetime, I will have witnessed one of, if not the most important scientific discoveries ever. What I object to is needless scientific hypotheses gaining traction in the public mind when there’s absolutely no evidence to support them. Yes, panspermia is an incredible idea, and yes, exerts wildly pontificating about its mechanisms and implications is important, but in my opinion it is far more important to study and concentrate on the origins of life from those basic, and it would seem abundant, ingredients, and once proven, continue to unravel more mysteries of the mysteries of the solar system and beyond.

In short, to answer Universe Today’s article title of “Life on Ceres: Could the Dwarf Planet be the Root of Panspermia?” No, probably not. And what’s wrong with the idea of life starting here?

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