Pluto’s departure from its title as a <keyword id="20111358" type="General" weightage="20" keywordseo="planet" source="keywords">planet</keyword> not only hurt fans of the now dwarf, but it also changed the pecking order of planets within our <keyword id="52393" type="General" weightage="20" keywordseo="solar-system" source="Orion">solar system</keyword>. At only a third the size of the <keyword id="19912640" type="General" weightage="20" keywordseo="Earth" source="keywords">Earth</keyword>, <keyword id="19901068" type="General" weightage="100" keywordseo="Mercury" source="keywords">Mercury</keyword> had automatically become the smallest planet in our solar system, ripe for bullying by Jupiter and the other giants patrolling around our Sun. But alas, while Mercury’s minuscule appearance might make it an easy target, it wasn’t always this tiny, it turns out. Mercury, the smallest and closest planet to the Sun, has long captivated scientists with its extreme conditions and mysterious features. With temperatures swinging from scorching heat to freezing cold and a surface scarred by craters, understanding Mercury's composition and formation has proved challenging. Further, to actually get to Mercury is a mammoth task by itself. Since the planet is so close to the Sun, it takes a tremendous amount of effort to oppose the star’s gravity when near the planet. This also means a mountain of fuel is needed to decelerate spacecrafts enough so they can insert themselves into Mer-dog’s gravity without suffering a meteor’s fate. But that doesn’t mean we’ve stopped trying. <keyword id="19935155" type="General" weightage="20" keywordseo="NASA" source="keywords" meta.keywordsubtype="org" meta.entityname="NASA" meta.hostid="261" meta.entityid="NASA">NASA</keyword> has managed to fly two missions close enough to map the planet, which just made things even curiouser. For starters, they found that, for whatever reason, Mercury has an absurdly gigantic <keyword id="20060547" type="General" weightage="20" keywordseo="core" source="keywords">core</keyword> compared to its <keyword id="1609094" type="General" weightage="20" keywordseo="mantle" source="Orion">mantle</keyword>, while its crust is paper-thin — relatively speaking. The other nearby rock-based planets, such as Venus, Earth and Mars, all sport baby cores surrounded by a thick molten mantle. Further, analysis of Mercury revealed that it has an unusually high concentration of thorium, an element that should have evaporated in the extreme heat of the planet. Last, but not least, scientists found that, similar to Earth, Mercury too is surrounded by a magnetic field. This suggests that its inner workings might be very similar to ours, and even be made of the same stuff as our core. To keep himself from pulling his hair out, planetary researcher Nicola Mari decided to take a closer look at the planet. Forgoing fancy space-faring rockets and opting for cars and planes instead, his journey took him to Cyprus, a Mediterranean island that used to be at the bottom of the ocean 90 million years ago. The area’s rugged terrain unearthed a geological treasure trove: boninite rocks, born from our Earth’s oozing mantle. Through meticulous analysis, Mari and his team confirmed that these rocks suspiciously mirrored Mercury's chemical makeup almost exactly. The composition of elements such as magnesium, aluminum and iron was the exact same as that seen on the crust of the big-cored planet. The reason this is so significant is because boninites are formed from lava that erupts from a shallow point in our Earth’s crust. If Mercury’s rocks were also formed from its mantle in similar ways to our own, it means that something could have happened that blew away the majority of its crust, leaving behind the thin exterior we see now. Something catastrophic like an interplanetary <keyword id="19979441" type="General" weightage="20" keywordseo="collision" source="keywords">collision</keyword>, perhaps. This catastrophic clashing theory has been in the works for a while now, and planetary scientists think that Mercury might have started off being as big as the Earth. Most of its crust was wiped away post-collision, leaving what we see today. The journey to decipher Mercury's secrets is far from over. With <keyword id="21312858" type="General" weightage="20" keywordseo="BepiColombo" source="keywords">BepiColombo</keyword>'s — a joint space endeavor by the <keyword id="20681418" type="General" weightage="20" keywordseo="European-Space-Agency" source="keywords" meta.keywordsubtype="org" meta.entityname="European Space Agency" meta.hostid="261" meta.entityid="European Space Agency">European Space Agency</keyword> and Japan — scientific operations on the horizon, the stage is set for a new era of discovery. As Mari ventures forth to explore other terrestrial analogues, the cosmos awaits with its myriad secrets, ready to be unveiled one rock at a time. These findings are based on a BBC article that can be accessed <a href="https://www.bbc.com/future/article/20240410-mercury-the-solar-systems-smallest-planet-may-once-have-been-as-large-as-earth" data-type="tilCustomLink">here</a>.

An interplanetary collision might have shrunk Mercury to its current size, scientists think

Imagine yourself as an extraterrestrial tourist, taking a well-deserved break on <keyword id="6359982" type="General" weightage="50" keywordseo="earth" source="Orion">Earth</keyword> after countless hours on your home <keyword id="46100" type="General" weightage="20" keywordseo="planet" source="Orion">planet</keyword>. As you approach Earth after a million-light-year journey, you expect to see the familiar blue dot. To your surprise, you encounter what appears to be Earth's <keyword id="42440" type="General" weightage="50" keywordseo="moon" source="Orion">moon</keyword>, isolated in the vastness of space. Although you might initially think there's been a cosmic mix-up, the reality is that you've stumbled upon <keyword id="6372165" type="General" weightage="100" keywordseo="mercury" source="Orion">Mercury</keyword>, the closest planet to the Sun. The confusion is understandable since Mercury and Earth's moon share striking similarities, including size and a landscape covered in craters. But there's more to this similarity than meets the eye. Both worlds boast towering mountainous ridges that stretch across thousands of kilometres — an intriguing result of their billion-year-long cooling process. <cmsannotation type="cmsannotation" annotationid="A Planet in Contraction and Its Battle Scarps" comment="subhead" text="A Planet in Contraction and Its Battle Scarps">A Planet in Contraction and Its Battle Scarps</cmsannotation> While missions to explore the moon's surface are numerous, the same cannot be said for Mercury. However, older observations continue to unveil the planet's secrets, and the latest discovery indicates that Mercury is shrinking, with its most recent contraction occurring more recently than previously believed. Unlike Earth, Mercury features an outer crust encasing a molten metal mantle, with a crucial difference: its crust doesn't break into tectonic plates like ours. Consequently, as its molten interior cools and contracts (similar to how mercury in a thermometer shrinks with decreasing temperature), Mercury's outer shell attempts to contract as well. However, this solid and singular crust resists shrinking in the same manner. As energy accumulates, sections of the crust begin to push against each other, forming the snake-like ridges along the surface, giving the planet a wrinkled appearance. A similar process occurs on the Moon, albeit to a lesser extent. Although these structures, known as 'scarps,' suggest Mercury is undergoing contraction, they do not precisely reveal how long this tectonic activity has been ongoing. To determine that, scientists turn to impact craters on the planet's surface. Given that Mercury experiences frequent planetary impacts, researchers can estimate the age of a particular scarp by assessing whether it intersects with older craters. Additionally, if newer craters appear on top of the scarps, it implies that the scarps formed before the associated impacts. However, a team of scientists has introduced a new method for dating these scarps, shedding light on the last time Mercury contracted. This novel technique involves examining relatively smaller fractures on the scarps, known as "grabens." <cmsannotation type="cmsannotation" annotationid="Closing Graben Holes and Filling Knowledge Gaps" comment="subhead" text="Closing Graben Holes and Filling Knowledge Gaps">Closing Graben Holes and Filling Knowledge Gaps</cmsannotation> As portions of Mercury's crust push against each other, some strips may become trapped and bend, leaving long, crack-like fractures on the scarps — similar to how a slice of bread bends, creating cracks along the fold. Interestingly, this phenomenon is also observed on the Moon. As Mercury cools, seismic activity causes the planet to shake, potentially loosening boulders and debris that eventually find their way into these grabens. Impacts from extraterrestrial bodies can also dislodge and shift terrain in a similar fashion. Therefore, the presence of unfilled grabens suggests that not much time has passed since their formation. Armed with this innovative parameter, scientists embarked on a quest to identify such surface anomalies on Mercury's crust. They identified not just one or two but a remarkable 48 large scarps marked by tiny grabens. An additional 244 scarps displayed "probable" grabens, though further examination is required to confirm their nature — perhaps the <keyword id="6973137" type="General" weightage="50" keywordseo="bepicolombo" source="Orion">BepiColombo</keyword> mission, operating in Mercury's orbit since early 2016, could aid in this endeavour. The team determined that most of these grabens are likely less than 300 million years old, indicating that Mercury's most recent contraction occurred relatively recently — possibly within the last few million years. The next piece of this puzzle will likely emerge once BepiColombo provides clearer images of Mercury. Until then, we hope our alien tourist enjoys the renowned Earthly beaches.

Mercury's shrinking history revealed through surface craters: insights from the planet's shriveling past

<ul class="summary-list"><li><a href="https://www.businessinsider.com/spaceship-flying-by-venus-wednesday-could-help-look-alien-life-2020-10">BepiColombo</a>, a <a href="https://www.businessinsider.com/astronaut-photo-aurora-from-international-space-station-2021-9">European</a>-<a href="https://www.businessinsider.com/spacex-starship-dearmoon-crew-japanese-astronaut-soichi-noguchi-yusaku-maezawa-2020-9">Japanese</a> spacecraft, flew past <a href="https://www.businessinsider.com/how-see-conjunction-mercury-jupiter-saturn-planetary-trio-2021-1">Mercury</a> for the first time Friday.</li><li>The probe beamed back beautifully clear images of the <a href="https://www.businessinsider.com/scientists-animation-reveals-planets-wildly-different-speeds-2021-8">planet's</a> cratered, moon-like surface.</li><li>It's set to fly past <keyword id="6372165" type="UNKNOWN" weightage="60" keywordseo="mercury" source="Orion">Mercury</keyword> five more times before falling into the planet's orbit in 2025.</li></ul>Mercury is finally back in the spotlight, with a space probe zooming past its cratered surface for the first time in six years.As it flew past Mercury on Friday, the <keyword id="12243980" type="UNKNOWN" weightage="60" keywordseo="bepicolombo" source="Orion">BepiColombo</keyword> spacecraft snapped the above photo from 1,500 miles (2,418 kilometers) away, about 10 minutes after skimming past the planet. The image shows ancient lava fields in Mercury's northern hemisphere.This is BepiColombo's first good look at its target planet since it launched in 2018. The spacecraft is a joint mission of the <keyword id="11921802" type="UNKNOWN" weightage="60" keywordseo="european-space-agency" source="Orion">European Space Agency</keyword> (<keyword id="12243982" type="UNKNOWN" weightage="60" keywordseo="esa" source="Orion">ESA</keyword>) and Japan Aerospace Exploration Agency (<keyword id="12243981" type="UNKNOWN" weightage="60" keywordseo="jaxa" source="Orion">JAXA</keyword>). It's on track to fall into orbit around Mercury in 2025, when it will map the planet's surface, analyze its composition, and sense its magnetic field. Scientists hope all this data will reveal the history of the closest planet to the sun.But first, BepiColombo has to swing past Earth, Venus, and Mercury, leveraging the <keyword id="11910186" type="UNKNOWN" weightage="60" keywordseo="planets" source="Orion">planets</keyword>' gravity to pull itself toward its ultimate orbital path. The spacecraft has already flown past Earth and Venus. Friday marked the first of six Mercury flybys."The flyby was flawless from the spacecraft point of view, and it's incredible to finally see our target planet," Elsa Montagnon, the mission's spacecraft operations manager, said in a <a href="https://www.esa.int/Science_Exploration/Space_Science/BepiColombo/BepiColombo_s_first_views_of_Mercury">press release</a>.The last time a spacecraft flew this close to Mercury was in 2015, when NASA's Messenger probe took one last look at the planet's craters before crashing into its surface.<h2>BepiColombo's footage shows Mercury fading into the distance</h2>BepiColombo's Mercury photos are so detailed that scientists can identify particular craters, named Rudaki, Lemontov, and Calvino.<div type="image" title="mercury grey cratered surface past spacecraft annotated with crater names" height="1024" width="1024" msid="86763065" hostid="261"></div>But BepiColombo isn't even using its best lens yet. The images from Friday's flyby come from its black-and-white monitoring cameras, but the spacecraft also has a high-resolution camera suite that it will deploy once it finally achieves Mercury orbit.The ESA assembled 53 images from BepiColombo's flyby into a video, below, to show the planet fading into the distance as the spacecraft zipped away.<iframe width="560" height="315" src="https://www.youtube.com/embed/GdOLeGeqAEI?start=17" frameborder="0"></iframe>At its closest approach, the spacecraft was just 124 miles (199 kilometers) above Mercury's surface - but it was on the side of the planet farthest from the sun, engulfed in nighttime darkness.BepiColombo didn't get a good look at Mercury until it had already zipped past and the planet's sunny side came into view. The closest image in this sequence is about 620 miles (1,000 km) from Mercury."It was very exciting to see BepiColombo's first images of Mercury, and to work out what we were seeing," David Rothery, who leads the ESA's Mercury Surface and Composition Working Group, said in the release. "It has made me even more enthusiastic to study the top quality <keyword id="11896083" type="UNKNOWN" weightage="100" keywordseo="science" source="Orion">science</keyword> data that we should get when we are in orbit around Mercury, because this is a planet that we really do not yet fully understand."

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An interplanetary collision might have shrunk Mercury to its current size, scientists think

Ankush Banerjee

Mercury's shrinking history revealed through surface craters: insights from the planet's shriveling past

Ankush Banerjee

A European-Japanese spacecraft snapped the clearest photo of Mercury in 6 years as it flew past the planet

Morgan McFall-Johnsen