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Could Earth have sent life to Jupiter's moon Europa?
by David Appell, Phys.org

edited by Sadie Harley, reviewed by Robert Egan
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Could Earth have seeded Jupiter's moon Europa with bacterial life, where
it could have taken hold in Europa's ocean and perhaps evolved into
something more? That's the hypothesis of a new paper in the
International Journal of Astrobiology by Zaza Osmanov of the Free
University of Tbilisi in Georgia.

Osmanov calculates the chance that dust particles containing living
bacteria were ejected from Earth's gravitational well and traveled to Jupiter's icy moon Europa, where they could have landed undestroyed and
made their way through cracks in Europa's ice, beneath which lies a vast
sea that scientists believe could harbor life.

The possibility of panspermia, bringing simple life to Earth from
elsewhere in the universe, has been discussed for decades. Dust,
meteoroids, asteroids and comets might all have contained life forms as
they crashed into Earth.

The hypothesis is impossible to test experimentally, but in a paper
published in the International Journal of Astronomy and Astrophysics,
Osmanov, who is also affiliated with the E. Kharadze Georgian National Astrophysical Observatory, calls this the "reverse panspermia problem"
and calculated that "in 5 billion years dust grains can travel in the interstellar medium at distances of the order of hundreds of parsecs."

Also, given the distribution of stars in the Milky Way, "particles
emitted by every single planet will reach as many as 105 stellar
systems." Moreover, Osmanov found that from a single planet, life can be transported to about a thousand star systems.

The red line is the trajectory of a dust grain traveling from Earth, at
1 astronomical unit (AU), to the vicinity of Jupiter at 5 AU, using the parameters and assumptions utilized in the text. Credit: Used with
permission of Zaza Osmanov.
How the Europa case works
Using techniques similar to those in his earlier paper, Osmanov
considered Earth as an origin of dust grains, and Europa, with its
unique ice and ocean features, as their end point. Osmanov breaks his
analysis into three parts:

Could dust grains carrying life have escaped Earth's gravitational
field, and in what abundance?
Could such dust grains have landed on Europa in a way that didn't
destroy them, and in what numbers? And 3. If they landed, could such
grains have permeated Europa's thick crust of ice and reached its liquid surface?
Dust particles about a micron (a millionth of a meter) in size can
contain packed bacteria of about the same size. Moreover, for the
bacteria to survive any journey, their temperature cannot exceed about
300 Kelvin (about 27-#C).

Dust grains are carried aloft by atmospheric turbulence; considering the energy imparted to one at 150 kilometers (93 miles) in altitude, as
through a collision with cosmic dust, Osmanov's 2025 paper allowed him
to calculate a maximum imparted velocity of the dust grain of 14 km/s at altitude, which exceeds Earth's escape velocity of 11.2 km/s.

More simple physics shows the particle would have a velocity of 8.4 km/s
when far from Earth, about 10% faster than the International Space
Station circles the planet. This would be happening for the entire 3.5
billion years that simple life has existed on Earth.

From Earth to Europa
After leaving Earth, three forces act on the dust particles: the
pressure of radiation from the sun, the gravitational force of Jupiter
(which dominates the sun's gravitational force after the grain has
traveled about 97% of the sun-Jupiter distance), and the average drag
force of the interplanetary medium in the solar system.

Osmanov solves the dust grain's equations of motion to find that its
velocity at Jupiter is 20.1 km/s. The impact of the grain on Europa is
at a maximum when it comes directly downward relative to the moon's
surface. Using the dust grain's specific heat, he finds that only grains
that come in at a very low anglerCo1 degree relative to the surfacerCowill survive the impact, meaning only about three in a thousand bacteria
packs survive the landing.

A flux of about one particle per square centimeter per second leaves
Earth through a collision with cosmic dust in the atmosphere, or about 5
x 1018 total particles per second, ejected equally in all directions.
Using geometry to find the fraction of dust particles that enter
Jupiter's gravitational zone, Osmanov finds that about 300 million such particles from Earth should reach Europa's surface every second.
(Author's note: Much larger than I would have guessed!)

Besides those above, Osmanov uses two other results from the scientific literature: Bacteria that land on Europa's surface undergo
"deactivation" in about 10,000 years, and about 20% to 40% of the moon's
ice, which is 30 million to 80 million years old, undergoes fracturing
from tidal heating and tidal friction from the titanic forces of Jupiter.

Simulations have found that regions of the ice can melt through in about
1,000 years, carrying bacteria down to the ocean surface, with broader
holes tens of kilometers wide occurring in about 10,000 years.

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What it could mean
Putting all these results together, Osmanov finds that "the total number
of particles during the mentioned period is of the order of (3-8) x
1023," or close to a mole of particles. This, he concludes, "strongly
suggests the likelihood of life being present in the subsurface ocean of Europa if the biological and biochemical conditions are compatible with Earth-originating life, which would require a new series of
investigations to determine."

We should be able to ascertain the presence of life on Europa when the European Space Agency's nuclear-powered Europa lander launches in 2027. Prototype drills tested in Antarctica were able to drill through 30
kilometers (19 miles) of ice in 300 days, and, if successful, would be
the first mission to directly access Europa's ocean and look for signs
of life.

Written for you by our author David Appell, edited by Sadie Harley, and fact-checked and reviewed by Robert EganrCothis article is the result of careful human work. We rely on readers like you to keep independent
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Publication details
Zaza Osmanov, Earth as a potential source of life for Europa's
subsurface ocean, International Journal of Astrobiology (2026). DOI: 10.1017/s1473550426100354

Journal information: International Journal of Astrobiology

Key concepts
Interplanetary dustSpace probes
Who's behind this story?
David Appell
David Appell is an Oregon-based freelance science writer whose work has appeared in Scientific American, New Scientist, Physics World, and The Washington Post. He holds a Ph.D. in physics from Stony Brook
University. Full profile raA

Sadie Harley
BSc Life Sciences & Ecology. Microbiology lab background with
pharmaceutical news experience in oil, gas, and renewable industries.
Full profile raA

Robert Egan
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full
profile raA

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