Wandering planets, the smell of rain and more reader feedback

Free-range planets

Astronomers are puzzling over some space oddities: planets that don’t orbit stars. In “Wandering worlds” (SN: 4/4/15, p. 22), Ashley Yeager explored how these lonely rogues may alter the definition of a planet.

Tim Geho wanted to know more about how scientists locate homeless worlds. “Where does the light come from that allows rogue planets to be seen, either directly or via gravitational lensing?” he asked. “Is there some sort of fluorescence or luminescence involved or is [light] reflected from distant suns?”

Some rogues can be imaged directly because big planets can emit their own heat, Yeager says. Telescopes detect this heat as infrared light. Identifying a planet with gravitational lensing is also possible. In this case, astronomers use light from a distant star to infer the existence of a planet. First they track the movement of the star. From the viewpoint of Earth, when the star passes behind some unseen object, the hidden object’s gravity will bend the star’s light. How much the object bends the light reveals the object’s mass. If the mass is similar to the mass of a planet, then astronomers assume that the unseen object is a planet.

Readers also had their own suggestions for what to call these rogues. Jeff Barry jokingly proposed naming them “nibirus,” after the mythical doomsday planet that is supposed to crash into Earth. John Turner commented, “Some sources refer to these nomadic bodies as ‘planemos.’ I notice we’re avoiding using that word in this article, though it’s been used in Science News pieces in the past. What gives?”

Planemo never became widely used in the astronomy community, according to Penn State astronomer Kevin Luhman . He suggests sticking with brown dwarf, while others, like Michael Liu at the University of Hawaii in Honolulu, prefer the term free-floating planet.

New thoughts on old tools

Developing new categories for types of stone tools could help anthropologists craft a more accurate view of hominid evolution, Bruce Bower reported in “Reading the stones” (SN: 4/4/15, p. 16).

Discussions on Facebook and Twitter centered on how difficult it would be to re-create some of the tools. Some readers, like Grink, declared confidently, “I can make that.” Others thought the process would be challenging. “It’s a very difficult technique,” wrote Shashank Ac. “Most modern humans would not last a day in the Stone Age.”

Mark S. took the idea a step further, suggesting a Paleolithic reenactment week: “Have the specialists get together and try to hunt, butcher and live as putative Stone Age peoples would. It would probably shed all sorts of light on what tools were really important and under what conditions. Anyone caught ordering pizza would lose their publication rights.”

The scent of rain

Andrew Grant explained how falling water drops can kick soil chemicals into the air, creating that well-known poststorm earthy aroma, in “Why rain smells like that” (SN: 4/4/15, p. 5).

The story confirmed what reader Bo Grimes had long suspected: “Ever since I first noticed the phenomenon as a child, I assumed chemicals were released from the soil, though I probably thought of it in terms of splashed dirt.” Commenter Zk10 wrote, “For whatever reason, the earthy, natural smell of raindrops on hot sand has a wonderful calming effect on me. These smells are so faint you do not even realize they are there. You just feel better. Nice to know the science behind it.”


In “An oil spill’s aftermath” (4/18/15, p. 22), U.S. District Judge Carl Barbier’s ruling about the amount of oil released in the 2010 Deepwater Horizon spill in the Gulf of Mexico was expressed incorrectly. The judge ruled that 4 million barrels of oil exited the reservoir but that, after accounting for oil collected at the site, 3.19 million barrels was discharged into the Gulf.

More Stories from Science News on Astronomy