HOW TO MAKE A PLANET
Scientists know that Earth was created in a cloud of particles that came together – but how? They have been unable to explain the process, but now a ‘planet delivery room’ has shown a familiar electrical phenomenon at play.
Take one high tower in Germany and thousands of glass balls...
In a cold dark spot far out in the universe, one dust grain strikes another. They stick together, and travel forward on their combined path through the darkness. Another dust grain joins them. Then another. And another. Once this process has repeated many billions of times, a ’baby planet’ will have formed. This may collide with other ’babies’, growing bigger all the time.
So was planet Earth formed. According to the theory, all planets begin their lives as dense clouds of dust and gas left over from star formation. So far so good, but there’s a problem. When scientists try to recreate the moment of birth in the lab, such small groups of dust grains reject each other. Why?
A breakthrough has been made inside a a 146-metre-high tower in Bremen, Germany, where scientists have made glass spheres collect as if they were baby planets. The scientists’ experiment seems conclusive proof of the planet formation theory, and the results may even suggest how life could germinate in other solar systems.
Planets are born in dust clouds
For centuries, astronomers have tried to solve the mystery of planet formation. In 1664, philosopher and mathematician René Descartes’ published his theory that the universe was once full of swirls of tiny particles that collected together to form the Sun, the Earth, and the rest of the Solar System. Descartes’ fundamental idea has aged well. Over the years, various hypotheses have been rejected, refined and exchanged, and astronomers now have a dominant theory known as ‘growth’. According to the growth theory, tiny dust and gas particles collide in the clouds surrounding new stars. The groups of particles grow ever bigger, finally forming a core that varies in size depending on the distance to the star. The closer to the star the planet forms, the smaller it becomes – just as we see in our Solar System.
To a large extent this simple explanation can explain planet formation. When the dust grains are smaller than 1mm, they collect due to a phenomenon known as adhesion, by which the charges of different materials’ molecules cause attraction. Adhesion is the same force that makes tiny dust particles collect into the fluff you find in the corners of your home. Once the groups of particles have grown to diameters of a few kilometres their gravity comes into play, the mutual attraction with other particle groups promoting more rapid growth.
However, the growth theory encounters a problem when experiments attempt to simulate the growth theory. The particle groups begin to reject each other when they reach diameters around 1mm, like snooker balls bouncing off each other. To solve the problem, scientists from the German University of Duisburg-Essen have tested a new hypothesis: static electricity can make the dust grains hook up like billions of tiny magnets, overcoming the problem of rejection.
Glass spheres catapulted in tower
If you rub a balloon against a wall, it will pass electrons to the wall, so the balloon becomes positively charged and the wall negatively charged. The phenomenon is also
known as static electricity, and it makes the balloon ‘stick’ to the wall. The same principle applies in a cloud of tiny particles that can ‘give’ and ‘take’ electrons, becoming positively and negatively charged, and subsequently collecting into tiny magnets. The principle was used by the German scientists in an effort to recreate the birth of a planet. The scientists placed glass spheres with diameters of 0.4mm in a chamber that was shaken for 10 minutes by means of a metal coil. The scientists directed a current through the coil, which surrounds a magnet. The electricity produced a magnetic field that reacted with the magnet, causing vibrations. The shaking in the chamber imitated the collisions between dust grains in the early childhood of a planet. The collisions between the glass spheres produced static electricity. Some of the spheres became positively charged, whereas others became negatively charged.
Experiment catapulted 120 metres
The scientists now had a collection of tiny particles that had built up static electricity, but they lacked another important step to recreate the conditions during the birth of a planet: the removal of gravity. The solution was the Bremen Drop Tower, which is 146 metres high and includes a chamber of 120 metres height that can be emptied of air almost completely. Scientists built their test set-up in 1.6-metre-high metal capsules that were hoisted to the top of the tower and dropped – or catapulted up only to fall down again. The acceleration means that the experiments are subjected to a mere one millionth of the usual gravity, so that they are effectively weightless.
The Bremen Drop Tower thereby imitates the conditions in space more easily and affordably than a flight in NASA’s famous ‘Vomit Comet’ reduced-gravity aircraft, and scientists from all over the world have been flocking to Bremen to test their hypotheses about weightless phenomena.
The Duisburg-Essen scientists used the Bremen Drop Tower to catapult the test set-up with glass spheres inside the tower. During the total 9.3 seconds it took the capsule to pass up and down again, the breakthrough happened. Static electricity made the weightless spheres collect in groups of 1000+ tiny glass spheres. Groups of this size are big enough to attract small particles solely by means of their gravity. The scientists had demonstrated that static electricity can explain how planets are born. The snooker problem is overcome.
Experiments assist search for life
Danish scientists have discovered that growing planets will continue to ‘attract’ dust even after having grown many kilometres in size – which doesn’t fit with the theory that planets such as Earth form in collisions between ‘baby planets’. The discovery provides new support for an extended theory of growth. And furthermore the Danish results indicate that Earth’s creation was unlikely to have been a unique event. Earth-like planets may have formed in the same way in other solar systems. And if the planets formed in the same way as Earth, the likelihood of them including liquid water increases. Astronomers now have an additional clue that could point them in the direction of other life in space.