Readers ask about the sun’s surface, landscaping Neandertals and more

Defining boundaries

NASA’s Parker Solar Probe is the first spacecraft to enter the sun’s atmosphere, crossing the boundary between interplanetary space and solar territory called the Alfvén critical surface, Lisa Grossman reported in “NASA probe is the first to visit the sun” (SN: 1/29/22, p. 10).

The probe’s solar visit allowed researchers to determine that the Alfvén critical surface lies about 13 million kilometers above the sun’s surface, Grossman reported. Reader Jeff Engel wondered what is considered the sun’s “surface,” given that the star is made of plasma and doesn’t have a distinct, solid surface.

In this context, the sun’s “surface” refers to its photosphere, from which most of the sun’s photons are emitted, Grossman says. The photosphere doesn’t have a solid surface either. Instead, it consists of a layer of gas and plasma about a few hundred kilometers thick.

Rising seas

The ice shelf holding Antarctica’s Thwaites Glacier back from the sea could collapse within five years, raising the risk of dramatic sea level rise, Carolyn Gramling reported in “Ice shelf could collapse within 5 years” (SN: 1/29/22, p. 12).

Gramling wrote that if the whole glacier were to slide into the ocean, it would raise Earth’s sea levels by 65 centimeters, or more than two feet. Reader Jim Schmitz wanted to know if water flowing into low-lying areas could possibly reduce the potential sea level rise.

Actual measurements of sea level rise do and will vary from place to place around the globe for various reasons, including expanding seawater, postglacial rebound, the rotation of Earth and sinking lands. The estimated sea level rise of 65 centimeters takes these factors into account, but none of them change the big picture, Gramling says.

As for already low-lying coastal areas, they won’t be able to disperse the rising waters; they’ll just become inundated themselves, Gramling says. “Melting of a major piece of an ice sheet will drown out everything else, pun intended.”

Ancient landscapers

Neandertals’ campfires, hunting and other activities may have helped transform an area in Europe from forest to open grassland around 125,000 years ago, making the hominids the first known to dramatically impact their environment, Bruce Bower reported in “Neandertals shaped European terrain” (SN: 1/29/22, p. 8).

Reader Morten Lindhard asked how much of that European landscape was opened with Neandertal-made fire, rather than by wild grazing animals.

Researchers don’t know for sure the percentage of the landscape transformed by fire, Bower says. A considerable area of the study site — which borders what is now a 24-hectare ancient lake basin and a nearby smaller basin in Germany — appears to have changed from forest to grassland. Extensive evidence suggests that ancient fires were the primary driver of this change, Bower says.

Several readers wondered if some of the Neandertal-made fires that cleared the forest may have been spread accidentally.

Scientists currently aren’t able to distinguish archaeologically between one or a few large fires that spread accidentally or many smaller, controlled campfires, Bower says. Signs of numerous campfires at the study site over a period of around 2,000 years suggest the latter. But there is always some uncertainty when reconstructing ancient behavior from archaeological evidence, he says.

Correction

President Bill Clinton called the deciphering of the human genome a “stunning and humbling achievement” in 2000, not in 2003, as stated in “Reading our genes” (SN: 2/12/22, p. 22).

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