Readers have questions about Ultima Thule, thirsty plants and vitamin D
Your letters and comments on the February 2, 2019 issue of Science News
Which way is up?
Initial observations of the Kuiper Belt object MU69, nicknamed Ultima Thule, suggested it had a snowmanlike shape. Ultima Thule’s two lobes are connected by a narrow neck that appears brighter than the rest of the space rock’s surface, Lisa Grossman reported in “New Horizons shows Ultima Thule looks like a snowman, or maybe BB-8” (SN: 2/2/19, p. 7).
“The photo of Ultima Thule was fascinating,” reader Thomas Ostwald wrote. “However, the explanation of the bright ‘neck’ as grains that rolled ‘downhill’ was a shock! Which way is up?”
Scientists consider the “up” direction opposite the pull of gravity on Ultima Thule. It helps to imagine you’re standing on the space rock, says James Tuttle Keane, a planetary scientist at the California Institute of Technology.
Walk on
Planetary scientist James Tuttle Keane drew a handy diagram of MU69 (not to scale) to help explain how gravitational forces influence the direction of “up.” He says it helps to imagine that you’re walking (or sledding) on the rock’s surface.
If you were standing on the bigger lobe (Ultima) and far away from the smaller lobe (Thule), you’d primarily feel the gravity of the big lobe and the surface would seem flat, Keane says. The pull of gravity would be perpendicular to the surface. The “up” direction would also be perpendicular to the surface, pointing away from gravity’s pull.
As you move closer and closer to the neck connecting the lobes, the gravitational pull from Thule would start to have a bigger influence than before. This would change the “up” direction. It would no longer be perpendicular to the surface.
When “up” isn’t perpendicular, there’s a slope. And so loose material on the surface of MU69 might “slump into” the neck region, Keane says. But that is just one of the many ideas scientists have for explaining Ultima Thule’s bright neck.
Additional observations indicate that the space rock is actually shaped more like two lumpy pancakes stuck together, rather than two snowballs. That might change scientists’ understanding of Ultima Thule’s gravitational field “a little bit,” Keane says. He and colleagues are working on a study to figure out what those changes could be.
Growth spurt
Tweaking tobacco plants’ genetic instructions boosted the efficiency of photorespiration. The modified plants grew roughly 40 percent bigger than plants that had not been genetically altered, Maria Temming reported in “A new way to genetically tweak photosynthesis boosts plant growth ” (SN: 2/2/19, p. 6).
Online reader Alice Friedemann asked if engineered plants would require more water than normal plants.
Generally, larger plants require more water than smaller plants, says Paul South, a molecular biologist with the U.S. Department of Agriculture in Urbana, Ill. These engineered plants “use the same amount of water per a given area or size, but since they are bigger they would use more water” than nonengineered plants, he says.
Deflating vitamin D supplements
Vitamin D supplements may have fewer health benefits than expected, Laura Beil reported in “Vitamin D supplements aren’t living up to their hype ” (SN: 2/2/19, p. 16).
Reader Sandra Mack thought that sunlight may deliver the health benefits that researchers were expecting from vitamin D supplements.
Both sunlight and supplements can make up for deficiencies, Beil says. But supplements are used in studies because they safely deliver vitamin D at higher levels. “Researchers still haven’t determined whether sunlight can safely deliver high amounts of vitamin D,” she says.
