At first glance, you wouldn’t think Hawaii has any connection at all with asteroid 2004 BL86, the one that missed Earth by 750,000 miles (1.2 million km) just 3 days ago. One’s a tropical paradise with nightly pig roasts, beaches and shave ice; the other an uninhabitable ball of bare rock untouched by floral print swimsuits.
But Planetary Science Institute researchers Vishnu Reddy and Driss Takir would beg to differ.
Using NASA’sInfrared Telescope Facility on Mauna Kea, Hawaii they discovered that the speedy “space mountain” has a composition similar to the very island from which they made their observations – basalt.
“Our observations show that this asteroid has a spectrum similar to V-type asteroids,” said Reddy. “V-type asteroids are basalt, similar in composition to lava flows we see in Hawaii.
The researchers used a spectrograph to study infrared sunlight reflected from 2004 BL86 during the flyby. A spectrograph splits light into its component colors like the deli guy slicing up a nice salami. Among the colors are occasional empty spaces or what astronomers call absorption lines, where minerals such as olivine, pyroxene and plagioclase on the asteroid’s surface have removed or absorbed particular slices of sunlight.
These are the same materials that not only compose earthly basalts – all that dark volcanic rock that underlies Hawaii’s reefs and resorts – but also Vesta, considered the source of V-type asteroids. It’s thought that the impact that hollowed out the vast Rheasilvia crater at Vesta’s south pole blasted chunks of mama asteroid into space to create a family of smaller siblings called vestoids.
So it would appear that 2004 BL86 could be a long-lost daughter born through impact and released into space to later be perturbed by Jupiter into an orbit that periodically brings it near Earth. Close enough to watch in wonder as it inches across the field of view of our telescopes like it did earlier this week.
The little moonlet may or may not be related to Vesta, but its presence makes 2004 BL86 a binary asteroid, where each object revolves about their common center of gravity. While the asteroid is unlikely to become future vacation destination, there will always be Hawaii to satisfy our longings for basalt.
Basalt is a hard, black volcanic rock with less than 52% silica. Because of this low silica content, basalt has a low viscosity (thickness), and so it can flow for long distances after erupting from a volcano. During an eruption, a basalt lava flow can easily move more than 20 km away from a vent. Basalt is the most common rock type in the Earth’s crust. In fact, most of the ocean floor is made up of basalt.
Basalt is made up of dark colored materials like pyroxene and olivine, but it also contains lighter minerals like feldspar and quartz. These crystals form because the lava cools slowly after erupting out of a volcano. Although a lava flow might look cool shortly after an eruption, it might take months or even years to cool all the way through. The crystals are bigger in the middle of a cooled lava flow because that part had longer to cool. If a lava flow cools quickly, like when it falls into a lake or ocean, it becomes a glass-like rock called obsidian. This is because the crystals in the rock don’t have time to form.
Shield volcanoes are made up entirely of basalt lava eruptions. A good example of this are the volcanoes Mauna Loa and Mauna Kea on the Big Island of Hawaii. Over hundreds of thousands of years, they have built up tall volcanoes that are extremely wide because of the fast flowing basalt lava.
Geologists have found large outpourings of lava covering hundreds of kilometers of land called flood basalt. The largest of these is known as the Siberian Traps in northern Russia. This is a region of 1.5 million square kilometers covered by basalt.
We have written many articles about volcanoes for Universe Today. Here’s an article about obsidian, and here’s an article about different types of lava.