by Kim Malville
October 3: Low on the western horizon look for the thin crescent moon above Venus
October 5: The moon has moved higher, now close to Saturn. Look below Saturn to see twinkling red Antares in the southwest.
October 20-22: The Orionid meteor shower will peak early in the morning of October 21. Its meteors should be visible for several days before and after, so get out and look.
October 26: Saturn can be seen above much brighter Venus in the southwest.
October 27: Saturn, Venus, and Antares will form a vertical line in the southwest. Binoculars should help to see Antares, about 30 minutes after sunset.
This past month has produced more than the usual spectacular astronomical discoveries—a galaxy made almost entirely of dark matter, a rocky planet orbiting the closest star to us, and the first views of Jupiter by the new Juno spacecraft.
A galaxy made of dark matter
Astronomers have recently discovered a galaxy as big as the Milky Way that consists almost entirely of dark matter. Only .01% of the galaxy is ordinary, visible matter like us. The other 99.99% of the matter is dark and invisible. This dark galaxy, with the wonderful name Dragonfly 44, is as big as the Milky Way but emits only about 1% as much light. A galaxy that big couldn’t possibly hold itself together with so few stars. There wouldn’t be enough gravity, and the stars would fly apart as they revolved around its center. It must be dark matter that is holding it together. In a sense this is not at all surprising considering that the universe has five times more dark matter than ordinary matter. Such dark galaxies cannot be easily found, and there must be many more out there in the cosmos. In the beginning of our universe, clumps of dark matter first formed and then drew in ordinary matter, which formed stars that lit up like Christmas tree lights. For some reason Dragonfly 44 didn’t attract ordinary matter. Here’s material for great science fiction. Instead of the scenario of a space craft mysteriously drawn into a black hole, there could be one pulled into a monstrous galaxy of dark matter from which it can’t escape. That galaxy may contain invisible clumps of dark matter and even be a voracious black hole consisting of dark matter lurking in its center.
Our nearest neighbor
The nearest habitable world beyond our Solar System might be right on our doorstep, astronomically speaking. Another one of last month’s discoveries is that the closest star to the earth, Proxima Centauri, has an Earth-sized planet orbiting about it, in its Goldilocks zone, rocky, and warm enough to allow liquid water on its surface. Proxima Centauri is 40 trillion km away and would take a spacecraft using current technology thousands of years to reach. Earlier this year, the billionaire venture capitalist Yuri Milner said he was investing $100m in studies to develop tiny spacecraft that could be propelled across the galaxy by lasers. These would travel at perhaps 20% of the speed of light, shortening the journey to a star like Proxima Centauri to perhaps 20 years.
The star Proxima Centauri is a member of a triple star system, which includes the much brighter double star system Alpha Centauri A and B. It is far from these two stars, which are visible in the sky in the depiction, and it takes some 500,000 years to orbit them. It is a red dwarf, much fainter than our sun. Because of that it uses up its available energy very slowly and will remain as bright as it is now for 4 trillion years, some 300 times longer than the age of the universe. By contrast, our sun will end its life as a normal star in some 5 billion years, ending normal life on the earth.
Proxima B has a mass 1.3 times that of Earth and orbits at a distance of about 4.5 million miles from the star, taking 11.2 days to complete one revolution. The distance between the star and its planet is considerably smaller than Earth’s separation from the Sun (92 million miles). But Proxima Centauri is much reduced in size and dimmer compared with our Sun, such that a planet can be nearer and still enjoy conditions that are as benign as those on Earth.
Researchers are presently looking to see if the planet crosses the face of Proxima Centauri as viewed from Earth. This kind of backlit observation could confirm not just the existence of an atmosphere but reveal the temperature of its night side and its atmospheric composition.
If there are lifeforms on Proxima b, they would have to withstand blasts of electrons and protons from its sun. Proxima is a well-known flare star, with a surface covered by sunspots. If the planet has a magnetic field like the earth, which seems reasonable, it could be protected from these particles. If that is the case, it should have some very dramatic auroras at its poles. As more telescopes are turned on this plant, we may be flooded with fantastic new information about our nearest neighbor in space.
Juno & Jupiter
Juno was injected into orbit around Jupiter on July 4 after a five-year journey. It has just completed the first of 36 dives, and it has sent back the first-ever images of Jupiter’s north and south poles. The images show storm systems and weather activity unlike anything previously seen on any of the solar system’s gas-giant planets. The north pole is bluer than the equatorial region of Jupiter, with its brilliantly colored cloud bands. You can see some unusual circular storm clouds over the pole, again unlike its equator. Juno also visited the south pole to catch pictures of its spectacular auroral zone. No other instruments, both from Earth or space, have been able to see the southern aurora. This crown of light is caused by high speed electrons precipitating downward from its Van Allen belt hitting hydrogen atoms, similar to what happens in the Earth’s aurora. Having spent a year in the Antarctic studying our southern auroral zone, I find this extraordinarily fascinating.