Ross 128

Due to Ross 128's proximity to Sol, the star has been an object of high interest among astronomers. It has been selected as a "Tier 1" target star for NASA's optical Space Interferometry Mission (SIM) to detect a planet as small as three Earth-masses within two AUs of its host star (and so some summary system information and images of Ross 128 are available from the SIM Teams). Astronomers are also hoping to use the ESA's Darwin group of infrared interferometers to analyze the atmospheres of any rocky planet found in the "habitable zone" (HZ) around Barnard's Star for evidence of Earth-type life (Lisa Kaltenegger, 2005).

The Star

This cool and dim, main sequence red dwarf (M4.1 Vn) has almost a third of Sol's mass, a tenth of its diameter, but only 33/100,000th of its luminosity. (Another reference suggests a tenth of Sol's mass, a fifth of its diameter, and 23/100,000 of its luminosity). Ross 128 would be only one of many unremarkable stars except that it appears to be a flare star as well as one of Sol's closest neighbors. In contrast to Proxima Centauri which is a "magnetically younger" flare star that is "activity saturated", however, Ross 128 is considered to be a more "evolved" flare star where its flare rate may have decreased somewhat with increased magnetic evolution (Andrew Skumanich, 1986). Moreover, dust has been detected around the star. It's variable star designation is FI Virginis, but other useful catalogue numbers include: FI Vir, Gl 447, Hip 57548, G 10-50, LHS 315, LTT 13240, and LFT 852.

Arnold O. Benz, Institute of Astronomy, ETH Zurich

High resolution and jumbo images (Benz et al, 1998).

Ross 128 is a flare star, like UV Ceti (Luyten 726-8 B)
shown flaring at left. UV Ceti is an extreme example
of a flare star that can boost its brightness by five times
in less than a minute, then fall somewhat slower back
down to normal luminosity within two or three minutes
before flaring suddenly again after several hours.

Life Around a Flare Star

Many dim, red (M) dwarf stars exhibit unusually violent flare activity for their size and brightness. These flare stars are actually common because red dwarfs make up more than half of all stars in the galaxy. Although flares do occur on our Sun every so often, the amount of energy released in a solar flare is small compared to the total amount of energy Sol produces. However, a flare the size of a solar flare occurring on a red dwarf star (such as Ross 128) that is more than ten thousand times dimmer than our Sun would emit about as much or more light as the red dwarf itself, doubling its brightness or more.

Flare stars erupt sporadically, with successive flares spaced anywhere from an hour to a few days apart. A flare only takes a a few minutes to reach peak brightness, and more than one flare can occur at a time. Moreover, in addition to bursts of light and radio waves, flares on dim red dwarfs may emit up to 10,000 times as many X-rays as a comparably-sized solar flare on our own Sun, and so flares would be lethal to Earth-type life on planets near the flare star. Hence, Earth-type life around flare stars may be unlikely because planets must be located very close to dim red dwarfs to be warmed sufficiently by infrared-rich star light to have liquid water (about 0.15 AU with an orbital period of less than 38 days for Ross 128), which makes flares even more dangerous around such stars. In any case, the light emitted by red dwarfs may be too red in color for Earth-type plant life to perform photosynthesis efficiently.

Hunt for Substellar Companions

A recent search for faint companions using the Hubble Space Telescope found no supporting evidence for a large Jupiter or brown dwarf sized object (Schroeder et al, 2000).