Today we had a great DTM seminar by Rachel Osten from the Space Telescope Science Institute (STScI). She talked about stellar activity and coronal mass ejections (CMEs).

A coronal mass ejection in time-lapse imagery obtained with the LASCO instrument. The Sun (center) is obscured by the coronagraph’s mask.

Osten pointed out that these huge eruptions from stars are important for several reasons. For example, the energy and frequency of CMEs depend on several properties of stars, including their age, rotation rates, and magnetic fields. In general, as stars age, their rotation rates drop, usually reducing the strength of their magnetic fields and the amount of CME activity. And so learning about CMEs can tell us about stellar evolution.

When a star fires off a CME, it typically flares or brightens a bit (see figure at right), and since we can’t see stars other than our Sun up close, we can use the temporary brightening of those stars to study their flare activity. Osten talked about one of her projects to use data from the Hubble Space Telescope to look for flare activity for many stars near the constellation Sagittarius.

That project had a surprising result: many stars that were thought to be older than the Sun actually showed MORE flare activity than they should have. This result might mean these stars actually have previously unknown binary companions that kept the stars spinning quickly and thereby keeping their flare activity up.

Stellar flares may also be important for planetary habitability. For example, a big stellar flare can actually disrupt the atmosphere of an Earth-like planet, perhaps even removing all of the life-protecting ozone.

Comparison of Venus’ and Earth’s topography. For Venus, orange represents the topographic highs, blue the lows. For the Earth, red represents the highs and blue the lows.

Today I saw an interesting talk about Venusian geophysics by Dr. Steve Mackwell.

Dr. Mackwell talked about how mountains, volcanoes, craters, and fractures in Venus’ surface allow scientists to infer the tectonic history of Venus.

For example, unlike the Moon, there aren’t that many craters on the surface of Venus, which should have accumulated with time as more and more asteroids and comets struck the surface. This lack of craters (along with widespread, large-scale volcanic features) suggest that Venus underwent a tremendous volcanic upheaval about a half billion years ago, during which global volcanic eruptions almost completely re-surfaced the planet.

Dr. Mackwell also discussed how his lab experiments in rock mechanics (in which he squeezes and heats rocks to determine their physical properties) have contributed to our understanding of Venus’ history.

For example, the flow of heat from Venus’ interior drives its geophysical activity and plays a key role in determining the strength of the rocks underlying the surface topography. Understanding the relationship between internal heat flow and rock strength, however, requires lab experiments such as Dr. Mackwell’s.