The 55 Cancri Extrasolar Planetary System

the sun-like star 55 Cancri and its five planets

55 Cancri is a sun-like star that is located in the constellation of Cancer. It is 41 light years away from Earth and is visible from Earth through a telescope or even a good pair of binoculars.

Astronomers believe that 55 Cancri is about the same age as our Sun and its mass is only slightly smaller than our Sun.

What makes 55 Cancri so interesting is that it has five planets in orbit around it. This suggests that the setup of our solar system probably isn't unique and that there may be many solar systems in the Universe similar to our own. This finding also increases the possibility that there may be other habitable planets besides Earth that are capable of supporting life.

The NASA images on this page depicting the 55 Cancri solar system are artists' conceptions of what the planetary system looks like. Astronomers don't actually know what the planets orbiting 55 Cancri look like because they haven't been able to see them. Because extrasolar planets are so far away, at this time astronomers can only use indirect measures to find them.

To find extrasolar planets astronomers look for stars that dim for a period of time. If a star dims, but then goes back to its original brightness, this indicates that a planet in orbit around it moved in front of it but has then moved past it.

artists conception of the 55 Cancri extrasolar system

They can also detect extrasolar planets by noticing a "wobble" in the star. This wobble or slight movement in the star is caused by the gravitational pull of a large planet in orbit around it.

Astronomers can determine a lot about extrasolar planetary systems using these indirect measures, such as the approximate size and mass of each planet and the star, and also their orbit.

For example, scientists know that the planets in orbit around 55 Cancri have a circular orbit like the planets in our solar system, as shown in the image depicting the planetary orbits of the 55 Cancri planetary system and our own solar system. The blue circles indicate individual planetary orbits. As you can see, four of the planets are in orbit fairly close to 55 Cancri, and only one orbits at a great distance from it.

two planetary systems - 55 Cancri and our solar system

The 5 Extrasolar Planets

Here is what astronomers know about the five extrasolar planets orbiting 55 Cancri:

The closest planet to 55 Cancri has about the same mass as Uranus and is located 5.6 million km (3.5 million miles) away from the star. It orbits the star in slightly less than 3 days.

The second planet is 17.9 million km (11.2 million miles) away from the star. It has about the same mass as Jupiter. It completes one orbit every 14.7 days.

The third planet from 55 Cancri is 35.9 million km (22.3 million miles) away. Its mass is about the same as Saturn's. It makes one complete orbit around the star every 44 days.

The fourth planet is 116.7 million km (72.5 million miles) from the star. This distance is similar to the distance that Earth is from our Sun (149.6 million km or 93 million miles). This planet's distance from 55 Cancri places it in the habitable zone - a zone in which it is likely that the temperature would permit the presence of liquid water. Scientists believe that liquid water is a necessary component to support the development of life. Astronomers believe that the planet may be similar to Saturn in composition and appearance, but only about half the size. It orbits the star every 260 days.

The fifth and most distant planet from 55 Cancri is 867.6 million km (539.1 million miles) from the star. It is a large planet with four times the mass of Jupiter (the largest planet in our solar system). The fifth planet completes one orbit every 14 Earth years.

Astronomers have only found five planets orbiting 55 Cancri so far, but there may be more planets that they haven't yet detected. So far, all of the planets found orbiting the star are large. Smaller planets would be harder for astronomers to detect, which means astronomers may not have found them yet.