It's official, folks. We're not alone.

On Tuesday, multiple channels broke the news that NASA has discovered the largest collection of solar planets yet. Some 41 light-years distant, we've found five planets quietly making their rounds about the star 55 Cancri -- second star to the left, and straight on till morning.

So what?
In an interview with PBS, Professor Geoff Marcy of the University of California, Berkeley, explains that NASA's discovery is significant for two main reasons. First, Cancri is "very similar to our sun -- the same mass, almost the same age, nearly the same chemical composition as our sun." Second, "this star harbors five planets. ... So we're beginning to see full families of planets orbiting other stars, giving us a sense that our own solar system is not unusual." Statistically speaking, the chances of life existing "out there" just went up.

So ... what does this have to do with stocks?
Oh. Well, basically, the increased probability that there's a "there" out there is going to increase people's interest in interstellar exploration. Over time, that means that more dollars (and euro, yen, and yuan) will be invested in space exploration -- and that can mean only good things for the companies involved in this endeavor.

Namely?
Tuesday's news has inspired me to do a little digging through the Fool archives, and a little more over at the SEC's, to try to figure out just who's who in the world of publicly traded space exploration. Herewith, a brief primer on the subject, beginning with the heavyweights:

Boeing (NYSE:BA)
The big name in institutionalized space exploration, Boeing classifies its space work under the rubric "Integrated Defense Systems -- Network and Space Systems." With $12 billion in sales last year, this business accounted for roughly one revenue dollar in five at the aerospace giant. Boeing's contribution to the space race takes the form of work on Delta launch vehicles, satellite systems, the International Space Station, and the space shuttle (in the form of delivering space payloads). Late last year, Boeing partnered with Lockheed to form the United Launch Alliance, which engages in "production, engineering, test, and launch operations associated with U.S. government launches of Boeing Delta and Lockheed Atlas rockets."

Lockheed (NYSE:LMT)
Speaking of Lockheed, its "Space Systems" division brought in $7.9 billion in revenue last year -- as with Boeing, about 20% of the company's total take -- from building satellites, "space transportation systems," and missile defense systems. Signature products include the new Orion crew exploration vehicle and Ares launch system, the Atlas V launch vehicle, and the Mars Reconnaissance Orbiter and Mars Phoenix Lander.

United Technologies (NYSE:UTX) and General Electric (NYSE:GE)
These two companies may lack the high-profile roles of Boeing or Lockheed, but without their engines, Boeing's and Lockheed's spaceships would have an awfully hard time getting where they're going.

Raytheon (NYSE:RTN)
Raytheon puts its cosmic activities within a division called "Space and Airborne Systems" (SAS). This unit generated $4.3 billion in sales last year -- 21% of Raytheon's total. On the ground, Raytheon's role seems to consist primarily of developing "satellite command and control software," as well as "information and network management." Systems, in other words. In terms of what happens in the air, the company makes the sensors, radars, and guidance systems that help get spaceships where they're going, and to see, hear, and talk along the way.

L-3 (NYSE:LLL)
L-3's role is similar to Raytheon's in that it works more on "spaceship guts" and leaves the building of the chassis to others. According to its 10-K, L-3 is responsible for communications equipment used on the International Space Station and the space shuttle. And just yesterday, L-3 announced that it will be helping out Alliant Techsystems by building the avionics to be used in Lockheed's Ares I launch vehicle -- a neat illustration of how, when a big project comes up, pretty much every company in this industry has a role to play, and a way to profit from it.

Northrop Grumman (NYSE:NOC)
Better known for its naval ships than its spaceships, Northrop got into the space game in earnest in 2002, when it acquired TRW's space and mission-systems businesses. Today, it calls this unit "Aerospace -- Space Technology." At just 11% of revenue, space occupies less, er, space at Northrop than at Boeing, Lockheed, or Raytheon. But at $3.3 billion last year, it's still a significant moneymaker. Northrop focuses on "spacecraft command and control systems," satellite communications, and a host of downward-looking programs, from monitoring the global environment to missile defense. And the more Northrop peers into space, the more it seems to like it. In July, the defense contractor bought private space-exploration pioneer Scaled Composites, the company behind SpaceShipOne.

T minus 3 days
I'm quickly approaching my word limit for today's column, so now that we've hit the biggest names, let's stop here for today. On Monday, I'll resume my own peering into space with a survey of a motley crew of assorted smaller names -- the privately owned companies, the unprofitable micro caps, and the Euro-players across the pond.

If you can't wait till Monday, though, feel free to click on over to Motley Fool Rule Breakers for a look at one last space contender. Take a free trial of the service, and we'll tell you which space stock we think is most likely to blast off.

Fool contributor Rich Smith does not own shares of any company named above. The Motley Fool's disclosure policy is out of this world.