Epsilon Eridani
Edwin Smolski
Eric Green
Search for the Origins of
Life Miniterm
3/14/02
Abstract and Background
In this report, we used one of the recently discovered extrasolar planets, and found information on it, as well as calculating temperatures the planet would have at different times in it’s orbit, with different albedos. While we are limited in actual visual observation of bodies orbiting stars, scientists have used indirect methods to discover bodies orbiting stars. The most common method is to find a “wobble” in the star, which would be caused by another mass in the system.
Luminosity of the star
The luminosity of a star is a measure of the star’s brightness. Measured in watts, this luminosity is dependent upon the radius of the star (squared) and the temperature of the star (to the fourth). The equations used below use an absolute magnitude measure, a logarithmic scale used to relate the absolute luminosity of the sun to the luminosity of the star in question (absolute meaning the measure of the star’s brightness from ten parsecs, or 32.6 light-years, away from the viewer).
This shows the luminosity of Epsilon Eridani to be 1.016x1026 watts, 34% as luminous as the sun (3.90x1026 watts).
Background of Epsilon Eridani System
The star Epsilon Eridani is the third closest visible star in the sky, at only 10.5 light years away. It is a very young star, at only 500 million to 1 billion years old, and it has about 85 % of the mass of the sun, 86-90 % of its mass, and only 34-35 % of its luminosity. Its location in the sky is to the right and below of Orion in the Eridanus constellation. Its relative magnitude, being so close to the Earth, is 3.72, while its absolute magnitude is 6.81. The star has large disk of debris far out, but the most unique and interesting attribute is an approximately Jupiter-sized planet that orbits the star.
The planet was officially discovered on August 11, 2000, although there were hints that a planet orbited the star several years before this. The team of astronomers who discovered the planet included Artie P. Hatzes, Barbara McArthur, Diane B. Paulson, and William D. Cochran, at the University of Texas McDonald Observatory. The planet is approximated to be 0.8 to 1.6 times the mass of Jupiter, and it travels at an average of 3.3 AUs from the star. A different measurement calculated the mass to be 1.2 times the mass of Jupiter (+/- 0.3). This average orbit is within the outer part of the asteroid belt, but the planet was also found to have migrated, causing an eccentric, cigar-shaped orbit with an eccentricity of e=0.6. It varies from about 1.3 AUs to 5.3 AUs from Epsilon Eridani, taking 6.8 years to complete a revolution. It took 6 sets of measurements from four different telescopes with three types of measurement techniques over about twenty years to verify the planet’s existence.
Planet Temperature
Planet temperature is the measure of the planet’s average surface temperature, in degrees Kelvin. This value is affected by three variables: the luminosity of the star (to the ¼), the distance from the planet to the star (to the negative ½), and the albedo of the planet (to the ¼). The albedo of a planet is the measure of the reflectivity of the planet
We selected three different albedos, each to represent different possible planet terrains. A reflective planet, possible with a watery or icy planet surface, or a cloudy atmoshphere, is represented by the albedo .75. A non-reflective planet, such as the surface of Mars, is represented by the albedo .25. In between these two extremes is the albedo .50, a planet that is only somewhat reflective, such as Earth, which has both rocky portions, and liquid water oceans and cloud cover. This covers the probable range of albedos that Epsilon Eridani may be.
We have also looked at the planet temperature in relation its distance from the star Epsilon Eridani. The 3.3 AU distance is the average distance of the planet from its star, while 1.3 AU is Epsilon Eridani’s semi-minor axis, and 5.3 AU is its semi-major axis.
|
|
d = 1.3 AU |
d = 3.3 AU |
D = 5.3 AU |
|
A = .25 |
Tp = 173.4 K |
Tp = 102.40 K |
Tp = 80.75 K |
|
A = .50 |
Tp = 156.7 K |
Tp = 92.47 K |
Tp = 72.97 K |
|
A = .75 |
Tp = 131.8 K |
Tp = 77.76 K |
Tp = 61.36 K |
Finding the star
The star chart (courtesy of The Sky) on the following page gives a diagram showing the position of Epsilon Eridani in relation to other constellations and other significant stars. We located Epsilon Eridani (labeled with a orange crosshair) using the star Rigel (labeled with a blue crosshair) as a reference point.
Conclusions
From our temperature calculations and the eccentric orbit of the planet, it is unlikely that our planet, Epsilon Eridani b, would sustain life. Its eccentric orbit would also tend to go against the possibility for life existing. It is however very likely that an Earth sized planet, orbiting inside this one, could sustain life. The very striking similarities of Epsilon Eridani to our own sun have many scientists optimistic.
Sources: http://www.solstation.com/stars/eps-erid.htm
http://exoplanets.org/esp/epseri/epseri.shtml
http://stardate.utexas.edu/pr/pages/20000807.html
http://www.astro.uiuc.edu/~kaler/sow/epseri.html
http://abcnews.go.com/sections/science/DailyNews/planet000804.html
