Discoveries of planets outside our solar system are coming so fast and furious that it has become difficult to keep track of the exact total.

SPACE.com asked Debra Fischer, a member of the U.S. team at the University of California, Berkeley, to help us nail down the real total. We also asked what the latest discoveries have taught her, and we pressed her for a glimpse of the future.

Fischer's team, led by Geoffrey Marcy at Berkeley and Paul Butler of the Carnegie Institution of Washington, finds planets by looking for a wobble in a star caused by the planet's gravity as it orbits. This so-called radial velocity method, or Doppler technique, is so far responsible for all initial detections of extrasolar planets.

SPACE.com: How many extrasolar planets are now properly documented by all groups?

Debra Fischer: There are 67 planet discoveries in refereed scientific journals, but 96 extrasolar planets have been announced.

SPACE.com: How many multi-planet systems are now known?

Fischer: Eight doubles. Two triples.

[Editor's note: And one with nine, our own]

SPACE.com: With your latest findings, what can you now say about the rarity or commonness of multi-planet systems?

Fischer: The fraction of multi-planet systems looks low right now, but this is deceptive. First, we don't announce a planet until at least one complete (or nearly complete) orbit has taken place. Planets at greater distances from their host stars have longer orbits (1 year for Earth, almost 2 years for Mars, almost 12 years for Jupiter, almost 30 years for Saturn).

We typically find the close-in planets first, but we see that many of these systems have longer-term velocity trends consistent with a distant planet. Statistically, about two-thirds of our "single" planets show signs of another companion. But we only see the tip of the iceberg with our technique: the most massive planets.

So, I suspect that every star that forms with one planet actually makes many planets. By the same token, I expect that many stars "without" (Doppler-detectable) planets actually have a host of planetary systems that would look quite normal relative to our own solar system. The signature of our own solar system is right at our lower detection threshold.

SPACE.com: More than half of your latest findings involve planets with orbits of 1 year or more. What does this say about the "normalness" of orbits that you'll likely find when technology allows the detection of smaller planets and planets farther from their stars?

Fischer: We've harvested all of the close-in, Jupiter-like planets in our sample of stars. [Some of these huge planets are closer to their stars than Mercury is to our Sun.] The only way to find more close-in, gas giant planets is to add new stars to our surveys.

Since more distant (longer orbital period) planets are harder to detect, the large numbers that we are finding suggest that "normal" orbits for gas giant planets may well be the longer period orbits [more similar to Jupiter]. Someday, we may be able to show that the roughly 5 percent of stars with close-in gas giant planets are relatively uncommon.

Fischer: In the last five years of transit surveys, the only transit detection was follow-up to a Doppler detection. But that detection showed that the transit technique was viable. The overwhelming problem, as I see it, will be to eliminate all of the "false positive" detections (such as grazing eclipsing binary stars) which will eventually number anywhere from a few to dozens of detections per month.

We may well have several hundred transit candidates in the next 5 to 10 years, but because most of the transit planets will orbit stars that are a few thousand light years away from us, follow-up to characterize most of these planets will be impossible.

There are a couple of other exciting techniques that will search for planets around stars closer than about 30 light-years. One of these techniques is high-contrast imaging. The plan here is to block out light from the host star and take deep exposures to directly image orbiting planets. One limitation of this technique is that it cannot reliably determine the mass of the orbiting points of light -- and planet mass is absolutely fundamental to understanding and characterizing extrasolar planets.

So the other technique that I'm excited about is the Space Interferometry Mission (SIM) which will measure absolute masses of planets orbiting nearby stars. Combining information from these two techniques is an unbeatable way for us to spy on solar systems orbiting our closest stellar neighbors.

SPACE.com: And finally, what can I say to our readers who wonder when the next planet(s) will be announced by your group?

Fischer: We have planets coming down the data pipeline in a steady stream. We pluck them out as soon as they complete one orbit, toss them in the pile of known planets and then keep searching for additional sibling planets around that same star.

Perusing our database, it appears that we will continue to find anywhere from one dozen to a few dozen planets per year for several more years.

Our group has recently secured funding for a dedicated telescope at Lick Observatory. With this telescope we expect to break new scientific ground: Instead of Jupiter-like planets (a few hundred Earth masses) we will be able to detect Neptune-like planets (17 Earth masses) out to the habitable zones around nearby stars.

We are very close to beginning site preparation work for the telescope, and team member Steve Vogt (who designed and built the spectrometers that we use at the Lick and Keck Observatories) has come up with a spectacular new spectrometer design. This ultra-efficient spectrograph is optimized for planet hunting; we're all shaking our heads in amazement.

The competition should be worried!

We're now searching for funding at about the $1 million level for this spectrometer (which will bear the name of the donor) to complete our new planet-hunting telescope.