According to <a href="">NASA scientists</a>, the Voyager 1 spacecraft entered interstellar space in August 2012, becoming the first spacecraft to leave the <a href="/our_solar_system/solar_system.html&edu=high&dev=1">solar system</a>. The space probe is about 19 billion km from the <a href="/sun/sun.html&edu=high&dev=1">Sun</a>.  <a href="/space_missions/voyager.html&edu=high&dev=1">Voyager 1 and 2</a> were launched in 1977 on a <a href="/space_missions/voyager.html&edu=high&dev=1">mission</a> that flew them both by <a href="/jupiter/jupiter.html&edu=high&dev=1">Jupiter</a> and <a href="/saturn/saturn.html&edu=high&dev=1">Saturn</a>, with Voyager 2 continuing to <a href="/uranus/uranus.html&edu=high&dev=1">Uranus</a> and <a href="/neptune/neptune.html&edu=high&dev=1">Neptune</a>. Voyager 2 is the longest continuously operated spacecraft. It is about 15 billion km away from the <a href="/sun/sun.html&edu=high&dev=1">Sun</a>.<p><small><em>Image courtesy of NASA</em></small></p>This historic image is the first ever taken from a spacecraft in orbit about <a href="/mercury/mercury.html&edu=high&dev=1">Mercury</a>, the innermost planet of the solar system.  Taken on 3/29/2011 by <a href="/space_missions/robotic/messenger/messenger.html&edu=high&dev=1">MESSENGER</a>, it shows numerous craters across the <a href="/mercury/Interior_Surface/Surface/surface_overview.html&edu=high&dev=1">surface</a> of the planet.  Temperatures there can reach over 800F because Mercury is so close to the Sun and rotates so slowly.  MESSENGER entered orbit around Mercury earlier in March 2011.<p><small><em>NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington</em></small></p><p>The United Nations <a href="" target="_blank">estimated</a> that between 1994-2015, there were 6,873 natural disasters worldwide, which affected 218 million people and claimed 1.35 million lives. </p>
<p>Check out the materials about natural disasters in <a href="/earth/natural_hazards/when_nature_strikes.html&edu=high&dev=1">NBC Learn Videos</a>, and their earth system science connections built up by the related secondary classroom activities.</p><p><small><em>NBC Learn</em></small></p>Greenland's <a href="">ice sheet</a> saw a record <a href="">melt</a> in July 2012.  Scientists studying this event have found that this melting event was triggered by an influx of unusually warm air and amplified by the presence of a blanket of thin low-level <a href="">clouds</a> which pushed temperatures up above freezing.  For more information see the <a href="">press release</a> from the University of Wisconsin Madison.<p><small><em>Image courtesy of University of Wisconsin-Madison</em></small></p>A <a href="">study</a> of over 40,000 written entries in Irish Annals and ice core measurements shows a strong correlation between <a href="">volcanic eruptions</a> and extreme cold weather in Ireland over a 1200 year period, from 431 to 1649.  During this time up to 48 volcanic eruptions were identified in Greenland ice core records through deposition of volcanic sulfate in annual layers of ice. Find out more about <a href="">volcanoes and climate</a>.<p><small><em>Image Courtesy of Marco Fulle</em></small></p>Scientists are concerned that melting Arctic sea ice will increase the amount of fresh water in the <a href="/earth/polar/arctic_currents.html&edu=high&dev=1">Beaufort Gyre</a>, which could spill out into the Atlantic and cause major climate shifts in North America and Western Europe. Watch the <a href="/earth/changing_planet/freshwater_arctic.html&edu=high&dev=1">Changing Planet: Fresh Water in the Arctic video</a>.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="">Woods Hole Oceanographic Institute</a>)</em></small></p>

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