Aug 17, 2017

Why is the solar corona so hot?

Our Expert Voices conversation about the 2017 solar eclipse.

The solar corona — the outer atmosphere of the Sun that is revealed so spectacularly during a total solar eclipse — is one of the great mysteries in space science. The biggest puzzle of all is its extreme temperature of several million degrees. Why is the corona so hot when the solar surface below is a comparatively paltry 6,000 degrees?

Most solar physicists believe the primary source of the heat is stressed magnetic fields that permeate the corona and impulsively release pent up energy when the fields reach their breaking point. Occasionally this produces giant explosions called solar flares and coronal mass ejections. But much smaller nanoflares are happening all the time — about a million per second across the Sun — each equivalent to the detonation of a 50 megaton hydrogen bomb.

Why it matters: The corona produces large quantities of X-ray and ultra-violet radiation that are absorbed in Earth's upper atmosphere. Variations in radiation affect the propagation of radio signals, which adversely affects communication, navigation, surveillance, and precision weapons guidance systems. The upcoming solar eclipse affords us a rare view of the Sun's atmosphere and a chance to study how it gives rise to nanoflares so that we can improve space weather forecasts.

Other voices in the conversation:

Go deeper

Coronavirus updates: Market ends worst week since financial crisis

Data: The Center for Systems Science and Engineering at Johns Hopkins, the CDC, and China's Health Ministry. Note: China numbers are for the mainland only and U.S. numbers include repatriated citizens.

The stock market ended its worst week since the financial crisis, prompting the Fed to release a statement. Meanwhile, the WHO warned that countries are losing their chance to contain the novel coronavirus and raised its global risk assessment to "very high" Friday.

The big picture: COVID-19 has killed more than 2,860 people and infected more than 84,000 others in over 60 countries and territories outside the epicenter in mainland China. The number of new cases reported outside China now exceed those inside the country.

Go deeperArrowUpdated 7 hours ago - Health

California coronavirus: Latest case has no recent history of international travel

Gov. Gavin Newsom. Photo: Kevork Djansezian/Getty Images

A new case of the novel coronavirus in California was announced on Friday after Gov. Gavin Newsom said Thursday that 33 people had tested positive for the virus, noting the risk to the public remains low.

What's new: An adult woman with chronic health conditions in Santa Clara County who "did not recently travel overseas" or come into contact with anyone known to be ill was confirmed to have contracted the coronavirus on Friday by CDC and California Department of Public Health officials.

Go deeperArrowUpdated 7 hours ago - Health

Big video game conference delayed amid coronavirus concerns

Photo: GDC

Next month's Game Developers Conference in San Francisco became the latest tech event to be cancelled or postponed amid growing concerns over the spread of the novel coronavirus.

The big picture: A growing number of events are being scrapped, including Mobile World Congress and Facebook's F8 developer conference. Some, like the giant SXSW event in Austin, insist they are moving forward.