Space Rocks From The Sky
- 9th Nov 2016
- Author: Tamela Maciel
What was the Earth like when it first formed? How has it grown into the living oasis of a planet that we know today? Where did Earth get all of the raw ingredients that are necessary to form life?
These fundamental, ancient questions about how we came to be can only be answered by looking out beyond Earth.
To understand ourselves, we must explore space.
4.5 Billion Year Old Time Capsules
That’s because Earth didn’t form in a vacuum (metaphorically speaking); it formed as a small, leftover bit of debris in the enormous cloud of gas, dust, and rock that surrounded our early Sun. This exact same debris cloud also formed the seven other planets, the asteroid belt, and the dwarf planets, icy comets, and other Kuiper belt objects that circle our star. The whole Solar System was built from the same basic building blocks.
On Earth, pristine examples of these basic building blocks are hard to come by. Weather and geology on the surface has warped, reshaped, and covered up the primordial stuff. But elsewhere in the Solar System, perfect time capsules do exist – time capsules which allow us to reach back 4.5 billion years ago to when the Solar System was first forming to see the stuff that we are made from.
Meteoroids and comets are two key examples. We think that these little bodies of rock and ice are as old as the Solar System itself, chunks leftover from that original debris cloud that never got scooped up into a planet.
But of course, the Solar System being the dynamic place that it is, meteoroids and comets move around, and sometimes a chunk of rock that’s been biding its time for more than four billion years is suddenly diverted onto a kamikaze course towards the surface of a planet.
Melted Asteroid Cores
Last week a new rock was found on the surface of Mars by NASA’s Curiosity rover – turns out this rock isn’t Martian though. Curiosity’s laser zapped the rock to test its composition and confirmed that the rock is an iron meteorite that likely fell from the sky many millions of years ago.
This was the first time that a meteorite on Mars has been laser-analysed for detailed study, and it’s fun to think that Curiosity is now acting out the same role that a meteorite-hunter here on Earth goes through when they find a strange new rock.
Iron meteorites are the most easily recognisable space rocks. Their smooth surfaces, magnetic properties, and bizarre shapes are dead giveaways that these rocks aren’t local.
It’s thought that iron meteorites are the dense, melted cores of bigger asteroids that have broken apart in a collision.
Moon Gardening
The Moon also suffers bombardment from space rocks, as is clear from its heavily cratered surface. But until recently, we hadn’t realised just how common new impacts are.
Scientists use the term ‘gardening rate’ to refer to how quickly the top few centimetres of lunar soil is churned and replaced by fresh impacts. Turns out that Moon gardening is happening at a rate 100 times faster than previously thought, thanks to new data from NASA’s Lunar Reconnaissance Orbiter. Since the Orbiter first entered orbit around the Moon in 2009, it has detected more than 200 fresh impacts, thanks to before and after photographs of new craters.
This means that crater-free areas on the Moon are probably younger than we think and won’t stay crater-free for long. Even the Apollo astronaut footprints may be gone in a few tens of thousands of years rather than the millions of years previously thought.
Comet Ingredients
When ESA’s Rosetta mission ended on 30 September 2016, it was a bittersweet moment.
For more than two years, this mission to a comet revealed so many telling clues as to where the organic materials and water on Earth may have come from.
The water found on Rosetta’s comet is slightly different than the water on Earth, leaving the link between comets and water on Earth still a mystery. But Rosetta did make the first clear detection of the simplest amino acid, glycine, on a comet. Glycine is the basis of many proteins here on Earth – perhaps it was a comet that brought glycine and other complex molecules to Earth in the first place.
The Solar System is a pretty mixed up place and always has been. As recent discoveries have reminded us, rocks and other materials are readily swapped between bodies. Perhaps rocks from space even provided the raw ingredients that sparked the formation of life here on Earth.
This is why it’s important to study other places in the Solar System.
Because those other places aren’t really other places. Everything formed from the same debris cloud as the Sun formed, and even after formation, all of the planets, comets, and meteoroids continue to swap material at surprisingly high rates. What’s mine is yours.
