Epsilon Eridani

Epsilon Eridani

Factual

Epsilon Eridani is a K2 star about ten-and-a-half light years from Earth, a bit cooler than our sun Sol and quite a bit younger (estimated to be about 800 million years, compared to our 4,500 million years). It features briefly in my novel The Chara Talisman. It's nearest stellar neighbor is a binary pair of red dwarf flare stars, UV Ceti (also known as Luyten 726-8) at just over five light years, but TauCeti, home (in T-Space) to Jackie Roberts and the Port Skead spaceport in Chara Talisman, is only a little further at five-and-a-half light years.

It's been known since 1998 to have at least one planet.. Astronomers deduced the planet's presence because of lumpiness in the cometary ring. As I write this on Oct 27 2008, NASA has announced that observations from the Spitzer Space Telescope indicate that e Eridani has two asteroid belts, which strongly implies the presence of more planets.

The above diagram shows what we think we know, or think we know, about the system so far. None of that excludes the presences of smaller (Earth-sized) planets within the inner asteroid belt, closer to the star, because they'd be too small to detect.. My story isn't obsolete yet. Because ε Eri (as it's typically abbreviated) is cooler than our own sun, habitable planets would be closer. A planet at a distance equivalent to between Mercury and Venus would see ε Eri as about the brightness of our sun from Earth, although specific temperatures would depend on other factors too (greenhouse effect, for one).

Fictional

There are other story implications. This is a relatively young system (this is factual) with a lot of asteroidal material, and being young, there are isotopes with relatively short half-lives that no longer exist (or exist in short supply) in the Solar system. Asteroid mining is a major industry. Somewhat higher levels of background radiation will likely mean that life on the terraformed planet has mutated more than usual, with interesting results.

The outer reaches of the system (that is, a distance corresponding to the out reaches of the Solar System's Kuiper Belt or inner Oort cloud) contains scattered gas and dust clouds which can present a minor hazard to warp navigation. Transit through such a cloud generally means a brief surge in background radiation, but unless something larger is struck, is relatively harmless, although sometimes alarming.

History

The Epsilon Eridani system is first visited by a Chinese expedition contemporary with the multi-national Alpha Centauri expedition and the first landing on Sawyers World.

This is mentioned briefly in epilog of Alpha Centauri: First Landing and in more detail in Alpha Centauri: The Return.

Later the system is settled, more or less, under the auspices of the Union de Terre (see below).

Planets

There is one terraformed, but "barely habitable", planet in the system. It is named Spitzer, after the space telescope which discovered the star's asteroid belts. When we meet Jackie Roberts in The Chara Talisman, she is on her way there.

The planet is smaller, cooler and dryer than Earth, but larger and wetter than Mars. The "barely habitable" is Roberts's opinion, but she comes from the overall warmer planet Skead, orbiting Tau Ceti.

In the below table, planet b is confirmed, planets d and c are strongly suspected, and Spitzer is (so far as we know) fictional.

planet	Distance(AU)	Period(days)	Mass	Diameter	Gravity
Spitzer	0.85	262	0.66 Me	0.9 Re	0.82g
Aegir (b)	3.39	2502 (6.85 yr)	493 Me (1.55 Mj)
d	~20	~97 yr	>300 Me (0.94 Mj)
c	~34	~220 yr	>100 Me (0.32 Mj)

(Note: days and years above are Earth days/years)