"Life on Mars," the 55th Carnegie International, is a thoughtfully orchestrated package that in turn surprises, implicates, amuses, communicates and baffles.

The title, the first to be given to an International, generated broad early interest in the exhibition. And its accompanying query -- "Are we alone in the universe?" -- provided a focal point to ponder for those speculating about content.

However, the actual questions on curator Douglas Fogle's mind are metaphysical rather than astrophysical: Are we alone on the Earth? What is the state of humanity in today's connected yet conflicted world? Has alien(ation) become our common condition?

The extent to which a particular artwork addresses such specific questions varies from central to oblique. The unifier is the curator's vision, which surfaces in the selected works and in the discerning way in which they are presented, whether setting a mood or revealing unexpected relationships that widen conversations initiated by the individual pieces.

Experimentation, expansiveness and vulnerability are elements that characterize the exhibition's high points, within the Carnegie Museum of Art and just a bit beyond.

Several works were commissioned for Pittsburgh, an action that introduces an element of immediacy generally lacking in large, institutionally based exhibitions regulated by external and internal logistics.

Among these is Doug Aitken's captivating video "Migration," surreal scenes of an assortment of animals -- buffalo, beaver, horse -- exploring, individually, various cookie-cutter motel rooms into which they've been released. Projected upon the front and rear exteriors of the museum, it not only arrests passers-by, but instigates thoughts about passive vs. active roles for architecture within its setting and for cultural institutions within their communities. (The video is turned on at dusk, about 8:30 p.m. recently, and its clarity sharpens as darkness settles in, about 9 p.m. It runs until 3 a.m. daily.)

Two sound installations by Susan Philipsz extend the International to the outdoor Sculpture Court and Carnegie Music Hall, the former transforming the open space with her mournful rendition of an American folk song. I didn't experience the latter because the Music Hall was closed for a previously scheduled event.

Scheduling conflicts also affect the exhibition's major film, the 98 minute-long "Pine Flat" by Sharon Lockhart, which I've seen only a part of. A Carnegie spokesperson says these spaces are no longer being rented out, but events scheduled before the rooms were allocated to International artists are being honored. Posting committed dates on the exhibition Web site would keep travelers who cannot return from being disappointed.

The most inventive use of atypical space is Mark Bradford's 20-foot-by-77.5-foot "Help Us," spelled out in white stone on the roof of the Scaife Galleries and visible only from the air. Inspired by the plight of Hurricane Katrina victims, it may have universal application if global warming waters lap at coastlines as predicted.

Bradford also exhibits imposing paintings that resemble aerial landscape views and have their genesis in egalitarian ephemeral materials.

It confounds me, however, that an artist who shows such sensitivity to form, subject and title would choose to product place. Even if one presumes that the upside-down Absolut Vodka bottle of "Across 110th Street" makes commentary about the way artists have routinely co-opted themselves by accepting commissions from the liquor company, Bradford faces a similar problem to that of feminist artists who felt they were taking ownership of women's bodies by presenting them as sex objects while disparaging men for doing so. The image speaks for itself, and it's much louder than any subtext. The market in art culture, like gender bias in the wider one, is so infiltrated that it escapes notice.

Blips like that are balanced by the overall humility of the exhibition, an admirably measured show that wears a mantle of reserve that's counter to larger societal currents but reflective of this particular time in the history of Western culture. Which is what, even with the inclusion of a handful of artists from elsewhere, this exhibition represents. But I digress.

The vulnerability of many works, intensified by their inherent poetry, is physical as well as dialogical, and invites intimacy.

For example, Ryan Gander's "A sheet of paper on which I was about to draw, as it slipped from my table and fell to the floor" comprises small, etched crystal spheres strewn across a gallery floor. Visitors stroll among them, at times inadvertently bumping one.

The tangled figures, collapsed upon themselves, of Thomas Schutte's "Zombie" series, similarly rest on the floor within brushing distance of visitors. And viewers have verified permission to enter the dream-like carpeted space of Mark Manders' "Room With Clothes, Belt, and Contact Lenses."

That vulnerability infuses Matthew Monahan's powerful distressed figures, and Lockhart's photographs of faux-confident youngsters.

Being humble doesn't rule out fun. Or exquisiteness.

Within his smart ordering, Fogle has a number of point/counterpoint pieces. Compare the cacophony of paint, color, bodies and media in Barry McGee's untitled installation that invigorates the walls of a high-traffic hall with the precision of Richard Wright's breathtaking feat, "No Title." Both works are on walls, about mark-making, infused with the hand, speaking to place and to contemporary expression. Both were commissioned. There similarities end.

Thomas Hirschhorn does the ultimate in walls, breaking all rules in his multi-roomed "Cavemanman," the dawn of culture morphed into its last stronghold against forces that threaten its destruction.

Superman's home is also in trouble, hanging on in the oxygenated bell jars of Mike Kelley's "Kandors," a multimedia, multisensory spectacle that is at once playful and sobering.

Perhaps what will linger longest with a visitor are the expressions on the faces of the individuals in Cao Fei's "Whose Utopia" and Phil Collins' "zasto ne govorim srpski (na srpskom)." Whether given the fanciful turn of the former video or the straightforward delivery of the latter, these are the witnesses to and participants in the era Fogle examines.

Here is Truth -- stark, unblinking.

The International continues through Jan. 11. For information: 412-622-3131 or www.cmoa.org.