Hunting for fallen stars

You can find meteorites the old-fashioned way, or you can make modern technology work in your favour. 

 
  rwarrin/Flickr  (CC BY-NC-ND 2.0)

rwarrin/Flickr (CC BY-NC-ND 2.0)

 

Field Studies is a monthly column by Clare Watson, who travels around Australia and the world exploring science by participating in studies, visiting research institutes, going on trips with scientists, and a lot more.

My backyard, any night of the week

It seems these days that we’re standing on shaky ground. Divided like the tectonic plates beneath us, the fault lines in the Earth’s crust, people are grinding against one another, trying to stand on top of the other’s values. We may live in foreign lands, perhaps we see the world differently from the place we each call home, but we stand under one sky.

One sky that envelopes our Earth, that makes you feel tiny when you stand cloaked in its darkness, that has billions more stars than goose bumps on your skin. Astronomers once mapped these stars on paper, then catalogued them with photographic glass plates negatives — now we can download a star map on our smart phones. 

Usually, when it comes to spending time outdoors, I’m all for leaving my phone at home alone but these star maps are a great pocket tool for budding astronomers. When you point the star map to the darkness above, constellations that have held mythical stories for millennia will be revealed. The star map swivels as you look through the viewfinder of your device, responding to the in-built GPS, compass and accelerometer in your phone. Turn the map to your feet and you can faintly see the would-be night sky that is currently drenched in daylight on the other side of the world. And just as the sun draws an arc over our days, the Earth spinning on its axis, the constellations will traverse the sky until they fall into the west horizon or fade with the dawn. 

While you’re there, stargazing, you might also spot a shooting star: a meteor burning across the sky. Meteors are extra-terrestrial rocky objects, fragments of asteroids, ensnared in Earth’s gravity. A meteoroid becomes a meteor when it hits the atmosphere at a blistering speed and the outer surface of the rock vaporises so that its bright tail is seen by a lucky few. Too small and the meteor will be obliterated into dust; but there might be some material at the core that withstands the fiery flight and, if it makes landfall, a meteorite lies in waiting.

Barren deserts are a good place to start looking, the vacant space thought to hoard fallen meteorites over time. In Australia, we have vast deserts that make up a large chunk of the continent; there’s also the semi-arid Nullarbor Plain that borders Western Australia and South Australia, and Kati Thanda-Lake Eyre, South Australia’s great salt lake, usually dry. The largest single meteorite found in Australia, the Mundrabilla iron, was discovered on the Nullarbor Plain in 1966, along with its smaller sibling. Named for the town near which it was found, many more fragments of the Mundrabilla meteorite have now been recovered, totalling almost 22 tonnes.

More than just a lump of rock, meteorites are relics of our early solar system — they are older than the Earth itself. The universe started with a bang 13.8 billion years ago; and the planets of our solar system slowly formed from a cloud of dust and gas. As matter clung together, gathering gravity, the planets became dominant objects and established their steady orbits around the sun. Now, between Mars and Jupiter hangs an asteroid belt, remnant debris in-limbo. Most meteorites that land on Earth are shards from these asteroids, the massive gravity of Jupiter hurling rubble in all directions as it passes by the belt. 

So precious are meteorites, essentially unaltered since their formation 4.5 billion years ago, that scientists dash out to the desert and spend days scouring the ground in search of new samples. Dr Andy Tomkins from Monash University, Melbourne, heads to the Nullarbor once a year with his band of geologists, students and retirees alike. When funding for the expeditions dried up in 2015, the group turned to crowd-funding for the 3,400-kilometre round-trip, a brainwave of PhD student, now Dr, Alastair Tait. 

Alastair tells me that the midday sun is best for spotting meteorites between the saltbush since there are no dark shadows to mistake for space rocks. Meteorites are sealed with a fusion crust, a shiny black outer layer that forms when molten metals solidify in the final seconds of flight. With this dark coating, meteorites stand out against the fair limestone plain, and most are also magnetic. But the midday heat is exhausting; instead, the group makes the most of the soft morning light, which means coffee all round. 

Alastair has always had an interest in space geology, Mars and meteorites. He studies meteorites because they could be refuge habitat for microbes in hostile environments — like the Red Planet. As they do on Earth, soil bacteria can infiltrate a meteorite after it has landed, eating away at metals in the porous rock and leaving a chemical fingerprint. The same types of meteorites that fall to Earth also land on Mars; several have been located by Martian rovers. If there is or was simple life on Mars, it might have a left a trace in these meteorites. Study these chemical traces of microbial life in the meteorites on Earth, as Alastair does, and we’ll know what we’re looking for on Mars.

From the other side of the Nullarbor, scientists from Curtin University, WA, are also on the lookout for meteors. Professor Phil Bland, planetary geologist and meteorite hunter, and his team have designed the Desert Fireballs Network (DFN) to keep more eyes on the sky. The network is a web of high-resolution cameras scattered across southern WA and South Australia, ready to capture fireballs as they tear through the atmosphere on entry. Some cameras are perched on tin roofs, others stand alone in the desert with only a solar panel for company. 

The wide-eye lenses, all 60 of them, give Phil and his team a tip-off to likely meteorites. The cameras are taking pictures of the night sky every 30 seconds but no human is scanning the images — the software system has been trained to recognise meteors. When one camera captures a fireball in the sky, it alerts other nearby cameras to confirm the sighting. If enough cameras in the network register the meteor, the system pings a message to the research team. 

Next, the Fireballs team triangulates the path of the meteor using footage from multiple viewpoints and, accounting for any wind blowing it off course, works out where the meteorite could have landed — but also where it might have come from in the solar system, giving a background story to newfound arrivals. 

For all the triple-checked calculations, success was sweet for Phil when, for the first time, he recovered a meteorite detected by the digital DFN in January 2016. He had to dig arms-length into the mudded surface of Kati Thanda-Lake Eyre to wrench it free — heavy rainfalls had smothered the impact site with sediment in the two weeks between detection and retrieval. It was a joyous confirmation that his system is working. The meteorite was named Murrili.

When you can’t join an expedition to the red interior, don’t worry, there’s the Fireballs in the Sky smart phone app. Amateur astronomers are invited to report their meteor sightings to the Fireballs team and people are chiming in from across the globe. That’s the wonderful thing about the night sky: it’s open to everyone. 

Incredibly, one meteorite sighted by a citizen scientist has recently been recovered. Carol Redford, head of the Stargazers Club WA, logged a meteor that fell in October when she saw it from her farm near Gingin, north of Perth. What started as one band of light, then exploded into several streaks, gifted an out-of-this-world meteorite that Carol later held in her own hands. The meteorite, Dingle Dell, had been found in less than a week in pristine condition thanks to Carol’s sighting, which matched the DFN footage. 

Murrili and Dingle Dell are now at home in the Western Australian Museum; it’s been a long journey and they can rest easy. Not so for Andy Tomkins, who has been back in the field. Last month he returned to the Nullarbor, which was unusually green after recent rains, and his team found over 40 meteorites, their best haul yet. Likewise, the cameras of the Desert Fireball Network are pointed skyward and with them, every night, are millions of eager eyes the world over.

 

 

Want to join the hunt for meteorites? Download the Fireballs in the Sky app and step outside tonight. The app gives you information on upcoming meteor showers and delivers updates on the Fireballs in the Sky team and their recent expeditions. You can even install a fireballs@home camera on your property to feed into the DFN, if you live in a suitable location. 

Come October, Intrepid Landcare are leading a camping adventure to the Warrumbungles National Park, north of Dubbo, NSW, to watch the Orionid meteor shower. In the meantime, you can also keep an eye on near-earth asteroids by following the NASA Asteroid Watch Twitter page.

Edited by Jack Scanlan