NASAâ€™s Parker Solar Probe is the first spacecraft to enter the sunâ€™s atmosphere, crossing the boundary between interplanetary space and solar territory called the AlfvÃ©n critical surface, Lisa Grossman reported in â€œNASA probe is the first to visit the sunâ€ (SN: 1/29/22, p. 10).
The probeâ€™s solar visit allowed researchers to determine that the AlfvÃ©n critical surface lies about 13 million kilometers above the sunâ€™s surface, Grossman reported. Reader Jeff Engel wondered what is considered the sunâ€™s â€œsurface,â€ given that the star is made of plasma and doesnâ€™t have a distinct, solid surface.
In this context, the sunâ€™s â€œsurfaceâ€ refers to its photosphere, from which most of the sunâ€™s photons are emitted, Grossman says. The photosphere doesnâ€™t have a solid surface either. Instead, it consists of a layer of gas and plasma about a few hundred kilometers thick.
The ice shelf holding Antarcticaâ€™s Thwaites Glacier back from the sea could collapse within five years, raising the risk of dramatic sea level rise, Carolyn Gramling reported in â€œIce shelf could collapse within 5 yearsâ€ (SN: 1/29/22, p. 12).
Gramling wrote that if the whole glacier were to slide into the ocean, it would raise Earthâ€™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 wonâ€™t be able to disperse the rising waters; theyâ€™ll just become inundated themselves, Gramling says. â€œMelting of a major piece of an ice sheet will drown out everything else, pun intended.â€
Neandertalsâ€™ 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 â€œNeandertals shaped European terrainâ€ (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 donâ€™t know for sure the percentage of the landscape transformed by fire, Bower says. A considerable area of the study site â€” which borders what is now a 24-hectare ancient lake basin and a nearby smaller basin in Germany â€” 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 arenâ€™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.
President Bill Clinton called the deciphering of the human genome a â€œstunning and humbling achievementâ€ in 2000, not in 2003, as stated in â€œReading our genesâ€ (SN: 2/12/22, p. 22).