Liquid water once on Mars
Eng/Arb إنكليزي عربي
ناسا تؤكد أن المريخ كان مغمورا بالمياه
قالت إدارة الطيران والفضاء
الأميركية ناسا إن كوكب المريخ كان يوما ما مشبعا بالماء لدرجة أن الحياة كان
يمكن بسهولة أن توجد عليه.
ورصد المستكشف الآلي أوبورتيونيتي أدلة واضحة على الهدف الأساسي لبعثة المريخ،
وهو أن المياه كانت تتدفق على سطح الكوكب الأحمر أو تشكل بركا عليه.
وقال المدير المساعد لناسا إد وايلر في مؤتمر صحفي إن أوبورتيونيتي هبط على
منطقة في المريخ كانت المياه تغمر سطحها "والأهم من ذلك أن المنطقة كانت بيئة
صالحة للسكنى".
وكان الروبوت الأميركي أوبورتيونيتي قد حط على سطح المريخ يوم 24 من يناير/
كانون الثاني لينضم إلى مستكشف آخر هو سبيريت الذي هبط على الكوكب في الثالث من
الشهر نفسه.
وتهدف مهمة سبيريت وأوبورتيونيتي اللذين لا يزيد حجمهما على حجم عربة الغولف
لدراسة جيولوجية المريخ خلال ثلاثة أشهر، وجمع معلومات بهدف تحديد ما إذا كانت
الشروط اللازمة للحياة متوفرة على الكوكب الأحمر أم لا.
وكانت ناسا أعلنت أن مركبة الفضاء سبيريت أرسلت صورة دقيقة لصخور مهشمة وتراب
لزج، في إشارة أخرى إلى احتمال وجود مياه على سطح المريخ. وأضافت أن الصور
الجديدة كشفت تفاصيل مذهلة عن وجود مادة تشبه الطمي وصخور تشبه تلك التي تتشكل
في المناطق الباردة من الأرض.
وأوضح العالم مايكل مالين أن وجود هذه الصخور المهشمة يشير إلى أن الماء كان
موجودا في وقت ما على سطح المريخ، غير أنه أبان أن تحطم الصخور ربما يكون ناجما
عن ظاهرة فضائية.
Liquid water once on Mars
Red planet may have been hospitable to life
- Mission accomplished: NASA scientists say the Mars rovers have found what
they were looking for -- hard evidence that the red planet was once "soaking
wet."
"We have concluded the rocks here were once soaked in liquid water," said
Steve Squyres of Cornell University. He's the principal investigator for the
science instruments on Opportunity and its twin rover, Spirit.
"The second question we've tried to answer: Were these rocks altered by
liquid water? We believe definitively, yes," Squyres said.
Squyres and other NASA officials made the announcement at NASA headquarters
in Washington, after several days of giving tantalizing hints that something
significant had been discovered.
"Three and a half years ago, in July 2000, we were on stage here to talk
about sending two rovers to get evidence of past water. NASA and its
international partners have turned those dreams to reality," said Ed Weiler,
NASA associate administrator for space science.
Scientists used instruments on board the golf cart-sized rovers to study the
composition of the rocks and soil on the planet. The rocks' physical
appearance, plus the detection of sulfates, make the case for a watery
history, and more important, an environment that could have been hospitable
to life.
While reporters pushed the scientists to come up with a "when" for the
existence of water on Mars, Squyres said it was very difficult to infer an
age simply by looking at pictures. He said a physical examination of samples
would be the only way to to get close to a time frame.
Squyres did offer a couple of scenarios on what might have happened that led
to the current discoveries:
One is that there was a volcanic eruption, possibly many eruptions, and
volcanic ash settled out onto the Martian surface. Subsequently, water could
have percolated through the ground, altering the ash to the chemical
composition it has today.
Another possibility, said Squyres, is that there was a salty sea at the
Meridiani Planum location, perhaps with currents, possibly even waves. As
the water evaporated, the salt would settle out.
"Both are fundamentally possible," said Squyres. "But we may never know."
Spirit and Opportunity were sent to opposite sides of the planet with the
possibility of investigating different types of terrain. Spirit, the first
rover to arrive on January 3, landed near the Gusev Crater, which may once
have held a lake.
But geologists and other researchers at NASA's Jet Propulsion Laboratory in
Pasadena, California, were thrilled when they saw the possibilities
surrounding Opportunity, which landed three weeks later. It landed inside a
small crater in the Meridiani Planum, one of the flattest places on the
planet. And its landing site was within driving distance for the spacecraft
to reach an exposed slice of bedrock.
Since its landing January 25, Opportunity has used the same tools as a human
field geologist would to determine the chemical contents of the rocks. Using
an alpha particle X-ray spectrometer, a device that can identify chemical
elements, scientists have identified a high concentration of sulfur in the
bedrock.
Another instrument on board, a Moessbauer spectrometer, has detected an iron
sulfate mineral known as jarosite. From their knowledge of rocks on earth,
scientists say rocks with as much salt as this Mars rock either formed in
water, or had a long exposure to water after they were formed. The
scientists say these rocks could have formed in an acidic lake or even a hot
springs.
Scientists say the case for a watery past is further strengthened by the
pictures taken by the rovers' panoramic cameras and its microscopic imager.
One target rock, named "El Capitan," is filled with random pockmarks.
Geologists say a texture like that comes from sites where salt crystals have
formed in rocks that have sat in salt water.
Scientists say they have gained other clues from the physical appearance of
the rocks. They see a pattern called "crossbedding," which is often the
result of wind or water moving across the rock's surface.
So what is ahead for the final few weeks of the rovers' operations on Mars?
"We need to take a close look at the outcropping, and broaden our view to
get a better understanding of the geology of the region, which is about the
size of Oklahoma," said Joy Crisp, project scientist at the Jet Propulsion
Lab. She said there are also plans to drive about 740 meters east to a
crater that has been nicknamed "Endurance."
And in the longer term?
"It's clear we have to do a sample return, both for the scientific side and
in preparation for human landing," said Weiler. He said future Mars missions
would also include miniaturizing equipment, and landing equipment that would
help prepare for the eventual landings of humans. That might include tests
for toxicity in the soil, and to determine if there are any materials that
humans might find useful when they do arrive.
The cost of the two rover missions is about $820 million. With solar panels
and lithium-ion battery systems aboard, each rover is expected to function
and communicate with earth for about 90 Mars days, known as "sols." That's
equivalent to 92 earth days.
