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1604
Kepler observes supernova. The telescope was invented a few years after
Kepler carried out extensive naked-eye observations of the supernova of
1604. Since the invention of the telescope no supernovas have been
observed in the Milky Way.
1609
Galileo uses telescope for astronomical observations. Galileo didn't invent the
telescope but he was among the first to use a telescope to examine the
heavens. He carried out important observations of the Sun, Moon, Planets,
and Stars. p. 51
1609
Galileo observes Moon. Galileo found that the Moon had mountains, valleys,
and plains like the Earth. He called the dark regions of the Moon maria, the
Latin word for seas. p. 52
c1610
Kepler discovers laws of planetary motion. Working with Tycho's
observations, Kepler discovers the shapes of planetary orbits, how the speed
of a planet varies as it orbits the Sun, and the relationship between orbital
distance and orbital period. p. 49-50, F 1.28, F 1.29
1610
Galileo observes phases of Venus. Galileo's found that Venus shows all the
phases from new to full. This observation was incompatible with the
Ptolemaic model of the solar system. p. 52, F 1.29
1610
Galileo discovers four largest satellites of Jupiter. Galileo found that Jupiter is
orbited by four large satellites, now called, collectively, the Galilean satellites.
This proved that at least some celestial bodies didn't orbit the Earth. p. 52
1620
Francis Bacon suggests that Earth's continents move about. Bacon noticed
that the eastern and western shores of the Atlantic were parallel and could
be fitted together. p. 162-163, F 5.11, F 5.12, F 5.13, F 5.14. A5.13
c1630
Descartes develops concept of inertial motion. Descartes believed that all
motion resulted from collision with particles called "corpuscles". In the
absence of such collisions, a body remains at rest. An object in motion
continues to move in the same direction at the same speed. p. 80-81, F 2.1
1632
Galileo publishes "The Dialogue". The Dialogue, although superficially a
balanced debate about the merits of the geocentric and heliocentric models
of the solar system, was in fact a powerful argument for the ideas of
Copernicus. Galileo was brought before the Inquisition and spent the last
nine years of his life under house arrest. p. 53.
16401700
Maunder minimum. During the Maunder minimum almost no spots were seen
on the Sun. This was also a time of cold climate in Western Europe and North
America. p. 349, F 11.25
1654
Bishop Ussher uses Bible to calculate age of Earth. From the chronology of
Biblical events, Ussher concluded that the Earth was created in 4004 BC. p.
160
1659
Christiaan Huygens realizes that the "appendages" of Saturn are rings.
Huygens watched the appendages disappear in 1665 and reappear several
years later. He realized that the appendages were really flat rings that
disappeared when viewed edge on. p. 283, F 9.12
1665
Giovanni Cassini discovers Great Red Spot of Jupiter. Although its size
and darkness have changed with time, the Great Red Spot has been
continuously present since the time of Cassini's discovery. p. 274-275,
F 9.1
1666
Robert Hooke shows that a central force leads to orbital motion. Hooke used
a pendulum to demonstrate to the members of the Royal Society that in
order to stay in orbit, the planets must be continually pulled toward the Sun.
p. 82.
16657
Newton discovers law of universal gravitation. When Cambridge University
was closed by the plague, Newton spent most of the next two years at his
family farm. During this period he made fundamental discoveries in optics,
discovered the law of universal gravitation, and invented differential and
integral calculus. p. 85, F 2.7
1667
G. Montanari notices brightness variations of Algol. Montanari saw that Algol
occasionally dropped to a third of its normal brightness. Later, the drops in
brightness were found to be caused by eclipses. p. 376
1668
James Gregory makes the first realistic estimate of the distances of the stars.
Gregory assumed that the other stars were just as bright as the Sun and
then calculated how distant they had to be to match their apparent
brightnesses. p. 356-358, F 12.1, F 12.2
1678
Christian Huygens proposes that light consists of waves. Huygens's ideas
were disputed by Newton, who proposed that light was mae up of a stream of
particles. p. 96-97. F. 3.1, A3.1
1682
Edmund Halley predicts return of Comet Halley. Halley noted that comets
with similar orbits had appeared in 1456, 1531, 1607, and 1682. He
proposed that these were all the same comet and that it would return in
1758 or 1759 - which it did. p. 309-310, F 10.8, 10.9, 10.10
1686
Newton publishes "Principia". Newton's monumental work described his
discoveries about gravity, motion and the orbits of the planets. p. 80-86, F
2.2, F 2.3, F 2.4, F 2.5, F 2.6, F 2.7, F 2.8
1718
Edmund Halley discovers stars move through space. Halley found that the
positions of stars change with time. He explained the changes in position as
due to the individual motions of stars through space. p. 463-466
1729
James Bradley discovers the aberration of starlight. Bradley found that the
positions of all the stars shift back and forth as part of an annual cycle
caused by the motion of the Earth about the Sun.
1781
William Herschel discovers Uranus. While measuring the directions and
brightnesses of stars, Herschel found a fuzzy spot that moved among the
stars. This was Uranus, the first planet that was not known to the ancients.
p. 54, p. 480
1781
Charles Messier prepares list of nebulae. Like other comet hunters, Messier
often mistook nebulae for comets. He compiled a list of 103 nebulae as an
aid to other comet hunters. This was the first list of nebulae. p. 141, Box F
4.5, p. 480 (left out F 16.1)
1783
John Goodricke discovers eclipses of Algol. Goodricke found that the
brightness declines of Algol occur at regular intervals. He proposed that the
brightness changes are due to eclipses of Algol by its binary companion. p.
372
1783
William Herschel discovers speed and direction of Sun's motion. Herschel
analyzed the motions of seven bright stars and showed that part of their
motions was due to the motion of the Sun through space. p. 371-373, F
12.10
1785
William Herschel uses star counts to map Milky Way. Herschel assumed that
the galaxy extended farther in directions in which he could see more stars.
He found the galaxy to be flattened with the Sun near the middle. p. 447448, F 15.4
1790
Pierre Simon Laplace proposes stars can produce black holes. Laplace
proposed that if a star is so compact that its escape velocity exceeds the
speed of light, then not even light can escape from the star. p. 431
1801
Giuseppe Piazzi discovers Ceres. Piazzi discovered Ceres, the first known
asteroid, on January 1, 1801, the first day of the 19th century. p. 304-307, F
10.4, F 10.5, F 10.6, A 10.6
1801
William Herschel shows many double stars are binaries. Herschel found that
for many pairs of stars, the orientation of the two stars changes with time.
The changes are a result of orbital motion. p. 374, F 12.13, A12.13
1802
William Wolleston sees dark lines in solar spectrum. Wollaston passed
sunlight through a prism and noticed that there were numerous dark bands
and lines in the spectrum. p. 111-112, F 3.15
1803
Meteorite shower at l'Aigle convinces scientists that meteorites have an
extraterrestrial origin. A careful investigation of the shower by Edouard Biot
convinced most skeptics that meteorites really do fall from the sky. p. 315316
1833
Denison Olmstead discovers shower meteors come from a common point in
the sky. Olmstead realized that the meteors seem to diverge from a point in
the sky because they originate in a swarm of meteoroids moving on parallel
paths through space. p. 315-316
1835
Gaspar de Coriolis discovers Coriolis effect. The Coriolis effect, the apparent
deflection of moving bodies due to Earth's rotation, explained many
atmospheric circulation patterns. p. 172-173, F 5.21, F 5.22
1837
h Carinae brightens to become second brightest star. h Carinae is normally
too faint to be seen, but between 1837 and 1860 it was the brightest star in
the sky.
1838
Friedrich Bessel, Wilhelm Struve, Thomas Henderson measure the distances
of stars. Bessel, Struve, and Henderson, working independently, almost
simultaneously measured the parallaxes, and hence the distances, of nearby
stars. These were the first measurements, rather than estimates, of stellar
distances. p. 356-358
1842
Christian Johann Doppler describes the Doppler effect. Doppler discovered
that the wavelength and frequency of a wave change if the source of the
wave moves toward or away from the observer. p. 114-115, F 3.18, A 3.18
1846
Calculations of Adams and Leverrier lead to discovery of Neptune.
Adams and Leverrier independently calculated the location of the
unknown planet, Neptune, that was required to explain discrepancies
in the orbit of Uranus. p. 291-292, F 9.23
1851
Jean Foucault uses pendulum to demonstrate Earth rotates. Foucault showed
that the pendulum swung in the same plane but the Earth rotated under it,
causing an apparent change in the direction of the pendulum's swing. p. 147
1859
James Clerk Maxwell discovers velocity distribution function for a gas.
Maxwell showed that the distribution of velocities of the atoms or molecules
in a gas depends on temperature and the mass of the molecules.
1862
William Huggins identifies chemical elements in stars. Huggins studied the
spectra of bright stars and found that the dark lines in their spectra matched
the wavelengths of atoms measured in terrestrial laboratories. p. 366-367.
1871
Asaph Hall discovers Phobos and Deimos. Remarkably, the prediction that
Mars had two small satellites was made by Jonathan Swift 151 years before
Hall's discovery. p. 264, F 8.24
c1875
Lord Kelvin and Hermann von Helmholtz estimate the age of the Sun. Kelvin
and Helmholtz independently calculated the length of time it would have
taken for the Sun to have shrunk to its present size. This time, called the
Kelvin-Helmholtz time, is about 20 million years. p. 336
1877
Giovanni Schiaparelli discovers "canals" of Mars. Schiaparelli reported thin,
dark lines crisscrossing the surface of Mars. The discovery raised the
possibility of intelligent life on Mars. p. 264-265, F 8.25
1879
Joseph Stefan finds the rate at which a blackbody emits energy. Stefan found
that the energy emitted by a blackbody increases as the fourth power of
temperature. p. 104-105.
1894
Wilhelm Wien finds how temperature affects the color of a blackbody. Wien
found that a blackbody gets bluer as its temperature increases. p. 104-105.
1900
Max Planck presents formula of spectral distribution of a blackbody. Planck
found the way that the energy emitted by a blackbody depends on its
wavelength and the temperature of the blakbody. p. 104-105.
1904
J. Hartmann finds interstellar absorption lines. Hartmann found a very narrow
line of calcium that didn't change in wavelength as the spectral lines from the
two stars in a binary star system shifted back and forth.
1905
Albert Einstein explains the photoelectric efect. Einstein explained that the
emission of electrons only by light at short wavelengths occurs because light
consistes of bundles of energy called photons. p. 97, F 3.2
1905
Einar Hertzsprung plots absolute magnitude versus spectral type.
Hertzsprung found that the stars are concentrated in a few regions of such a
diagram, which became known as an Hertzsprung-Russell (or H-R)
diagram. p. 377-379, F 12.17, F 12-18.
1905
Jacobus Kapteyn uses star counts to map Milky Way. Using star counts,
Kapteyn determined that the Sun lay 2000 pc from the center of a flattened
galaxy. p. 447-448
1913
Henry Norris Russell independently invents H-R diagram. The H-R diagram
became an important tool for understanding the evolution of stars. p. 377379, F 12.17, F 12-18
1915
Alfred Wegener proposes continental drift. Wegener noted the similarity of
rocks on opposite sides of the Atlantic Ocean and proposed that the present
continents had been part of a supercontinent that broke apart about 200
million years ago. p. 162-163, F 5.13
1916
Albert Einstein's general theory of relativity. Einstein explained that matter
curves space, causing bodies to move in ways we attribute to gravity. p. 527
1916
Karl Schwarzschild calculates geometry of black hole. Schwarzschild found
that if a massive body is compressed to a very small size it curves space
around it so severely that it forms a black hole. p. 431-432, F 14.12
1917
100" Mt. Wilson telescope completed. The Mt. Wilson telescope was the
largest optical telescope in the world for 31 years until the Palomar reflector
was completed.
1917
V. M. Slipher obtains radial velocities for 25 galaxies. Slipher found that 21 of
the 25 galaxies had red shifted spectral lines, indicating that they are moving
away from the us. p. 492-493, F 16.16
1918
Harlow Shapley find the size and shape of the Milky Way. Shapley assumed
that globular clusters are distributed uniformly about the center of the Milky
Way. From this, he found that the Earth is located 15,000 pc from the center
of the Milky Way. p. 447-449, F 15.6
1918
Annie J. Cannon and co-workers present thousands of stellar spectral
classifications in the Henry Draper Catalogue. Cannon and her co-workers
devised a classification system for stellar spectra and used it to produce a
catalog of spectra classifications for about 225,000 stars. p. 368-370, F 12.9
1920
M.N. Saha shows that the temperature of a star determines the appearance
of its spectrum. Saha showed that temperature differences rather are
responsible for the existence of different spectral classes of stars. p. 369
1920
A. S. Eddington proposes that fusion powers the Sun. Eddington suggested
that the fusion of hydrogen, the most common element in the Sun, into
helium provides the enormous energy output of the Sun. p. 336.
1923
Edwin Hubble shows spiral nebulae are galaxies. Hubble identified individual
Cepheid variable stars in spiral nebulae and used them to show that the
spiral nebulae are huge collections of stars far from the Milky Way. p. 481485, F 16.1, F 16.3, F 16.4, F 16.5, F 16.6, F 16.7, F 16.8, F 16.9.
1925
Cecilia Payne shows stars of different classes have essentially the
same chemical composition. Payne determined the chemical
composition of a number of stars of different spectral classes and
found that they were nearly the same. p. 369
1928
Arthur Holmes proposes mantle convection drives continental drift. Holmes
proposed that convenction currents in the layer Beneath the Earth's crust
push the continents about. p. 161, F 5.10
1929
Edwin Hubble discovers universe is expanding. Hubble found that the speed
of recession of galaxies increases with distance. He explained that this is due
to the expansion of the universe. p. 526-527, F 17.12
1930
S. Chandrasekhar shows white dwarf stars are made of degenerate electrons.
Chandrasekhar also showed that the more massive a white dwarf, the
smaller it is and that there is a maximum mass, the Chandrasekhar limit,
that a white dwarf can have. p. 422
1930
Clyde Tombaugh discovers Pluto. Tombaugh discovered Pluto by comparing
photographic plates taken of the same region of the sky about a week apart.
Pluto's image moved among the stars. p. 295, F 9.27, 9.28, 9.29
1930
Robert Trumpler discovers diffuse interstellar dust. Trumpler found that
distant star clusters were bigger than nearby star clusters. He reasoned that
this was because interstellar dust made distant clusters look fainter and,
hence, more distant. p. 458-460, F 15.13, F 15.14, F 15.15, F 15.16.
1931
Karl Jansky makes first radio astronomy observations. Jansky found that the
Milky Way galaxy is a source of radio emission. p. 469.
1937
Grote Reber builds first radio telescope. Reber built the first antenna
specifically designed for radio astronomy. Using the radio telescope, Reber
made the first map of cosmic radio emission. p. 137-138, F 4.12
1939
Robert Oppenheimer and George Volkoff calculate properties of neutron
stars. Oppenheimer and Volkoff calculated that a neutron star would be only
about 10 km in radius. p. 424-431, F 14.5, F 14.6, F 14.7, F 14.8, F 14.9, F
14.10, F 14.11
1944
H.C. van de Hulst predicts 21 cm line of interstellar hydrogen. van de Hulst
calculated that interstellar hydrogen atoms emit a spectral line at a
wavelength of 21 cm in the radio part of the spectrum. He suggested that it
would be possible to detect the 21 cm line using radio telescopes. p. 462463, Box F 15.1
1948
200" Palomar telescope completed. The Palomar telescope was the world's
largest high quality optical telescope for over 40 years. p. 136
1950
Jan Oort predicts existence of Oort Cloud of comets. Oort analyzed the orbits
of comets entering the inner solar system for the first time. He proposed that
these new comets originate in a cloud of comets tens of thousands of
astronomical units from the Sun. p. 307, F 10.11.
1951
Harold Ewen and Edward Purcell detect 21 cm line. Ewen and Purcell used a
radio telescope to detect emission from interstellar hydrogen atoms. p. 462463, Box F 15.1.
1951
Gerard Kuiper proposes existence of Kuiper Belt of comets. Kuiper proposed
that the comets with periods of less than 200 years originate in a flatted belt
of comets whose inner edge lies just beyond the orbit of Neptune. p. 311312, F 10.11.
1958
James Van Allen discovers Van Allen radiation belts. Explorer 1, the first
satellite launched by the United States, carried a Geiger counter built by Van
Allen. The Geiger counter showed that there are zones of trapped energetic
ions and electrons beyond Earth's atmosphere. p. 171-172, F 5.20.
1960
Frank Drake uses radio telescope to search for interstellar signals. Drake
searched at a wavelength of 21 cm for artificial signals from creatures on
planets orbiting two nearby stars. No signals were detected. p. 462-463, Box
F 15.1.
1960
Robert Leighton discovers solar oscillations. Leighton found that the Sun
vibrates at a variety of frequencies.
c1960
Harry Hess suggests mid-ocean ridges due to plate tectonics. Hess suggested
that the mid-ocean ridges occur where the ocean floor splits apart due to
plate tectonics and magma oozes out to form new ocean floor. p. 161-164, F
5.11
1961
Horace Babcock proposes model for sunspot cycle. Babcock's model involved
the twisting of solar magnetic fields lines because the rate of solar rotation
varies with solar latitude. p. 346-347, F 11.23, 11.24, 11.25
1963
Raymond Davis builds first solar neutrino telescope. Davis used a large tank
of cleaning fluid a mile deep in a gold mine to detect neutrinos produced in
nuclear reactions in the Sun's core. p. 339-340, F 11.12
1963
Maarten Schmidt shows quasars have large redshifts. Schmidt found that
previously unidentified lines in the the spectrum of the quasar 3C 273 were
actually redshifted lines of hydrogen. This showed that quasars are moving
rapidly away from us and are extremely distant. p. 500, Box F 16.2
1964
Arno Penzias and Robert Wilson discoverd cosmic background radiation.
Penzias and Wilson used a radio telescope to detect the highly redshifted
radiation from the early stages in the expansion of the universe. p. 521-522,
F 17.7, 17.8
1964
C.-C. Lin and Frank Shu explain spiral arms of Milky Way. Lin and Shu
explained that the spiral arms are the crests of density waves that rotate
through the galaxy. p. 449-451, F 15.7, F 15.8.
1965
Mariner 4 flies past Mars. Mariner 4 sent back pictures of Mars that showed a
deal planet whose surface resembled that of the Moon. p. 257-258, F 8.16
1967
Jocelyn Bell and Antony Hewish discover pulsar. Bell and Hewish
discovered regular pulses of radio radiation from a point in the sky.
The pulses were later attributed to beams of radiation emitted by a
rotating neutron star. p. 425, F 14.6
1969
Astronauts Edwin Aldrin and Neil Armstrong land on Moon. On July 20, 1969
Aldrin and Armstrong became the first people to land on the Moon.
1972
Last Apollo mission to Moon. Apollo 17 concluded the series of lunar landings
in which a dozen astronauts explored the Moon.
1973
Voyagers 1 and 2 reach Jupiter. The Voyagers used gravitational boosts from
their encounters with Jupiter to speed outward to encounters with other
planets in the outer solar system. p. 278, F 9.5
1974
Mariner 10 encounters Mercury. After passing Venus, Mariner 10 encountered
Mercury four times, sending back pictures of Mercury's surface. Mariner 10 is
the only spacecraft that has flows past Mercury.
1976
Vikings land on Mars. The two Viking landers safely touched down on Mars's
surface and, for several years, returned images of the surface, as well as
meteorological and seismic data. The Vikings also carried life-detection
experiments. p. 264-265.
1978
International Ultraviolet Explorer (IUE) launched. IUE has been in operation
for over 20 years, sending back ultraviolet spectra of celestial objects. p.
142-143, F 4.15
1978
James Christy discovers Pluto's moon, Charon. Chrisy noticed that Pluto's
image had a bump on it. The bump proved to be a satellite, Charon. p. 295296, F 9.27
1981
Very Large Array begins operations. The Very Large Array (VLA) is an array
of 27 radio telescopes that work together to produce radio images that are
comparable to those of traditional optical telescopes.
1981
Alan Guth proposes early period of inflation of universe. Guth proposed that
the a number of difficulties with the standard model of the expanding
universe could be explained by an enormous expansion very early in the
history of the universe. p. 532-533.
1986
Fleet of space probes encounters Comet Halley. A fleet of five space probes
flew past Comet Halley at distances as small as 600 km. Images sent back by
the spacecraft showed that the nucleus of Halley is very dark and larger than
anticipated. p. 310, F 10.10.
1986
Kamiokande neutrino telescope begins operating. Shortly after it was
completed, the Kamiokande telescope was one of two neutrino telescopes to
detect neutrinos from a supernova in the Large Magellanic Cloud.
1987
Supernova detected in Large Magellanic Cloud. The supernova, which
occurred in one of the nearest galaxies, was the first supernova in almost
400 years that could be seen without the aid of a telescope. p. 409.
1989
Hipparcos satellite begins making observations. Hipparcos made highly
accurate measurements of the positions and parallaxes of stars. p. 517.
1990
Magellan begins radar mapping of Venus Magellan produced an almost
complete radar map of the surface of Venus. p. 254-255, F 8.12, F 8.13
c1990
CCDs become the detector of choice in astronomy. CCDs are much more
sensitive than photographic plates and allow astronomers to detect very faint
objects.
1990
Hubble Space Telescope launched. The HST has produced images of
breathtaking clarity and has allowed astronomers to see light from more
distant objects than ever before. p. 142-143, F 4.15, F 4.16
1990
ROSAT launched. ROSAT produced X-ray images of hot, X ray emitting
objects. p. 142, F 4.15
1990
First Keck 10-m telescope completed. The Keck telescope, unlike most earlier
large optical telescopes, has a mirror made of many hexagonal segments.
There are now twin Keck telescopes on Mauna Kea. p. 125-126, p. 133, F 4.8
1990
Hubble Space telescope launched.
1991
Galileo obtains first up-close images of asteroid (Gaspra). The Galileo
spacecraft passed Gaspra at a distance of only 1,600 km. Images from
Galileo showed craters and groovelike cracks. p. 305, F 10.5
1993
Very Long Baseline Array completed. The Very Long Baseline Array (VLBA) is
an array of ten radio telescopes that work together to yield radio images with
even better resolution than optical telescopes can achieve.
1994
Fragments of Comet Shoemaker-Levy 9 strike Jupiter. Tides due to Jupiter
broke Comet Shoemaker-Levy 9 into at least 18 fragments that later struck
Jupiter, producing bright fireballs and new cloud features. p. 286
1995
Galileo probe enters Jupiter's atmosphere. An entry probe detached from the
Galileo spacecraft and parachuted into Jupiter's atmosphere. The probe sent
back data for about an hour before it was destroyed by high pressure and
temperature. p. 274, p. 281
1995
Infrared Space Observatory (ISO) launched. ISO obtained high resolution
infrared spectra and images of cool bodies and clouds of dust in the solar
system, galaxy, and beyond. p. 142-143, F 4.15
1995
Planets found orbiting stars like the Sun. Astronomers in the United States
and Switzerland reported the first detections of Jupiter-like planets orbiting
nearby Sun-like stars.
1996
Claim of evidence for fossil life in Martian meteoroid. A meteorite blasted
from Mars by an asteroidal impact was found to contain possible fossil traces
of ancient biological activity and life-like structures. p. 265
1997
Pathfinder lands on Mars, Mars Global Surveyor begins mapping of Mars. The
Pathfinder lander and the Sojourner rover it carried landed in an ancient
Martian riverbed. The Mars Global Surveyor is sending back pictures of Mars
that have unprecedented clarity and detail. p. 257-264
1998
Lunar Prospector obtains evidence of possible water on the Moon. p. 196
1998
Japanese researchers find evidence that neutrinos (possible candidate as
"dark matter") may have mass. p.495
1998
Gamma ray bursts proven to originate in distant galaxies, not our own, thus
deepening the mystery of their origin and power. p. 140.
1998
Astronaut John Glenn returns to space aboard the Shuttle Discovery in
October.
1999
NASA received a double set-back when first the Mars Climate Orbiter and
then the Mars Polar Lander space craft fail. P. 257 (Mars)
1999
Lunar Prospector intentionally crashed into Moon in attempt to identify water.
None is found. p. 188.
1999
NEAR spacecraft orbits an asteroid (Eros) for the first time. p. 304.
2000
Spacecraft NEAR-Shoemaker makes historic first landing on the asteroid
(Eros). p. 304.
2001
Leonid meteor storm on November 18. At times near the peak of shower, up
to 5 or 6 meteors could be seen per second.
2001
Sudbury neutrino detector in Canada demonstrates that neutrinos emitted
from the Sun's core change their type as they travel to Earth. This resolves
the many decade long mystery of the "missing solar neutrinos" and proves
these tiny particles have mass.
2002
Observations from a spacecraft orbiting Mars suggest large deposits of ice
may lie below the Martian surface.