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We're at a tipping point in human history,

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a species poised between gaining the stars
and losing the planet we call home.

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Even in just the past few years,
we've greatly expanded

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our knowledge of how Earth fits
within the context of our universe.

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NASA's Kepler mission has discovered

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thousands of potential planets
around other stars,

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indicating that Earth is but one
of billions of planets in our galaxy.

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Kepler is a space telescope

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that measures the subtle dimming of stars
as planets pass in front of them,

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blocking just a little bit
of that light from reaching us.

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Kepler's data reveals planets' sizes

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as well as their distance
from their parent star.

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Together, this helps us understand
whether these planets are small and rocky,

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like the terrestrial planets
in our own Solar System,

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and also how much light they receive
from their parent sun.

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In turn, this provides clues as to whether
these planets that we discover

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might be habitable or not.

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Unfortunately, at the same time
as we're discovering this treasure trove

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of potentially habitable worlds,

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our own planet is sagging
under the weight of humanity.

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2014 was the hottest year on record.

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Glaciers and sea ice that have
been with us for millennia

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are now disappearing
in a matter of decades.

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These planetary-scale environmental 
changes that we have set in motion

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are rapidly outpacing our ability
to alter their course.

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But I'm not a climate scientist,
I'm an astronomer.

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I study planetary habitability
as influenced by stars

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with the hopes of finding
the places in the universe

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where we might discover
life beyond our own planet.

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You could say that I look for
choice alien real estate.

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Now, as somebody who is deeply embedded
in the search for life in the universe,

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I can tell you that the more
you look for planets like Earth,

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the more you appreciate
our own planet itself.

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Each one of these new worlds
invites a comparison

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between the newly discovered planet
and the planets we know best:

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those of our own Solar System.

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Consider our neighbor, Mars.

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Mars is small and rocky,
and though it's a bit far from the Sun,

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it might be considered
a potentially habitable world

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if found by a mission like Kepler.

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Indeed, it's possible that Mars
was habitable in the past,

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and in part, this is why
we study Mars so much.

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Our rovers, like Curiosity,
crawl across its surface,

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scratching for clues as to the origins
of life as we know it.

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Orbiters like the MAVEN mission
sample the Martian atmosphere,

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trying to understand how Mars
might have lost its past habitability.

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Private spaceflight companies now offer
not just a short trip to near space

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but the tantalizing possibility
of living our lives on Mars.

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But though these Martian vistas

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resemble the deserts
of our own home world,

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places that are tied in our imagination
to ideas about pioneering and frontiers,

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compared to Earth

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Mars is a pretty terrible place to live.

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Consider the extent to which
we have not colonized

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the deserts of our own planet,

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places that are lush
by comparison with Mars.

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Even in the driest,
highest places on Earth,

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the air is sweet and thick with oxygen

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exhaled from thousands of miles away
by our rainforests.

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I worry -- I worry that this excitement
about colonizing Mars and other planets

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carries with it a long, dark shadow:

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the implication and belief by some

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that Mars will be there to save us
from the self-inflicted destruction

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of the only truly habitable planet
we know of, the Earth.

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As much as I love
interplanetary exploration,

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I deeply disagree with this idea.

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There are many excellent reasons
to go to Mars,

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but for anyone to tell you that Mars
will be there to back up humanity

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is like the captain of the Titanic
telling you that the real party

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is happening later on the lifeboats.

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(Laughter)

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(Applause)

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Thank you.

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But the goals of interplanetary
exploration and planetary preservation

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are not opposed to one another.

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No, they're in fact two sides
of the same goal:

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to understand, preserve
and improve life into the future.

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The extreme environments
of our own world are alien vistas.

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They're just closer to home.

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If we can understand how to create
and maintain habitable spaces

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out of hostile, inhospitable
spaces here on Earth,

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perhaps we can meet the needs
of both preserving our own environment

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and moving beyond it.

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I leave you with a final
thought experiment:

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Fermi's paradox.

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Many years ago, the physicist Enrico Fermi
asked that, given the fact

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that our universe has been around
for a very long time

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and we expect that there
are many planets within it,

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we should have found evidence
for alien life by now.

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So where are they?

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Well, one possible solution
to Fermi's paradox

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is that, as civilizations become
technologically advanced enough

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to consider living amongst the stars,

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they lose sight of how important it is

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to safeguard the home worlds that fostered
that advancement to begin with.

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It is hubris to believe
that interplanetary colonization alone

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will save us from ourselves,

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but planetary preservation
and interplanetary exploration

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can work together.

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If we truly believe in our ability

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to bend the hostile environments of Mars
for human habitation,

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then we should be able to surmount
the far easier task of preserving

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the habitability of the Earth.

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Thank you.

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(Applause)