Still, we have no direct evidence that we are, in fact, not alone. However, the Galaxy is a big place and we have only been looking with real instruments for 100 years or so.
The first step towards verification of other life in the Universe would be the discovery of other planetary systems around nearby stars. This has now been done unambiguously and those steps are detailed here.
What we know to date on more than a dozen nearby solar type stars is shown below:
The first object discovered in the above plot was 51 Pegasi in October of 1995. Since then, new systems have been discovered at the rate of a few per year.
The discovery of Jupiter mass planets around nearby solar mass stars is done by observing the radial velocity of the host star in an attempt to determine its reflex motion as its perturbed by a massive planet.
This technique is known as "Doppler wobble". For those of you with browsers that can run JAVA 1.1 applets, an interactive tutorial on this method is available.
In most cases, the observed data are adequately fit by a model with a single Jupiter mass planet causing the observed sinusoidal perturbation in the radial velocity of the host star. However, a recent analysis of the star Upsilon Andromeda by Geoff Marcy and colleagues has allowed for an improved fit by using a three component model. That fit is shown below:
The result is a Solar system in which there are three Jupiter like planets in orbit about a 1 solar mass star at distances less than the distance between our Sun and Mars.
What has therefore emerged from these studies is the indication that there is no one kind of Solar System arrangement in terms of where these massive planets are located. Indeed, it looks like our Solar System is somewhat unusual in that Jupiter is located at a relatively large distance from the Sun.
The radial velocity techniques used to detect these Jupiter size planets are nowhere near sensitive enough to detect planets of earth-mass size. Nonetheless, there is every reason to expect that smaller planets exist among the larger ones. Whether they are populated with an intelligence that makes their own web pages is unclear.
Meanwhile, back to our own Solar System ...
There is a lot we don't know about the details of how Solar Systems formed, although we think it proceeds by a multi-phase accretion process such as that shown below:
and later by imaging techniques in the Infrared :
The accretion process itself is rather inefficient leaving behind much cometary and meteoritic debris. Those objects are still around in our Solar System and occasionally impact the Earth. While this makes for really bad physics in Hollywood movies, it also is an important component to the evolution of life on the Earth as it introduces the element of random catastrophe.
Every once in a while a new asteroid is discovered and its initial error ellipse in its position always includes the Earth which usually evokes the following headline:
Here is what you can consider to be the UO Astronomer official statement on this Asteroid hysteria:
In early December 1997, Astronomers discovered a fast moving small asteroid. After 90 days of analyzing the orbit, it has been determined that this asteroid will have a near-earth encounter in 30 years. It is traditional that every new asteroid which is discovered has an error ellipse associated with its orbit that includes the earth. Hence, any time an asteroid is initially discovered, one can make the statement that there is some probability that it will impact the earth. A 90 day window in which to determine a 30 year orbit is an insufficient time to determine an accurate orbit and it is somewhat irresponsible science to do this and then issue a press release. This is similar to the cold fusion event of 1989.
The discovery of this asteroid is a triumph for new telescope and detector technology that is surveying the Solar System for small debris. Small objects like this are likely to be common and have simply escaped detection (and impacting the earth) for centuries, but that doesn't mean they aren't there. Currently there is grossly insufficient data to determine with any precision the orbit of this newly discovered object. Doubtless it will pass between the Earth and the Moon, as other objects have previously done. More years of monitoring will better establish whether its time to panic or not.
If panic is warranted, perhaps we need to move here: