My Science School

Many years ago, in 1610, Italian astronomer Galileo Galilei discovered the first moons beyond Earth. Those were the moons of the planet Jupiter, the largest planet in the solar system.

Planet Jupiter has 80 moons. There are many interesting moons orbiting the planet, but the ones of great interest to us on a scientific level are the first four moons discovered called the Galilean satellites. They are lo, Europa, Ganymede, and Callisto. Here we look at the four largest moons of Jupiter.

What is a Moon?

Moons are those celestial bodies that orbit planets and asteroids in the solar system. They are also called natural satellites. The Earth has one moon, whilst the solar system has more than 200 moons. Most of the major planets except Mercury and Venus have moons.

Jupiter and Saturn have the most moons. Four of Jupiter's moons are named after Galileo Galilei who first discovered them.

And how were the Galilean moons formed? According to scientists, the moons were formed out of the dusty disc left after Jupiter was formed.

lo

The most volcanically active body in the solar system, lo has its surface enveloped by sulfur. Jupiter's gravity causes "tides" that rise some 100 metres high on lo and lead to the generation of heat for volcanic activity.

Europa

Europa's surface is covered mostly by water ice. This moon is considered to have twice as much water as Earth.

Ganymede

The largest moon in the solar system, Ganymede is the only moon that has its own internally generated magnetic field. Did you know that this moon is even larger than the planet Mercury?

Callisto

The second largest moon of Jupiter, Callisto's surface is highly cratered and ancient. This moon is about half rock and half ice.

Picture Credit : Google 

On December 11, 1972, Apollo 17 achieved lunar landing. The sixth mission in the Apollo program to explore the lunar surface, Apollo 17, for now, is the last human expedition to the moon.

Apollo 11 will forever be remembered as the mission which enabled human beings to set foot on the moon, our natural satellite, for the first time. While the first will always remain the the same cannot be said for what is the last such mission, as future missions might take that place. But for the time being, Apollo 17 remains the last human expedition to the moon.

After the success of Apollo 11 in 1969, there were six more Apollo missions to the moon, five of which were successful. As U.S. President John F. Kennedy's objective of landing humans on the moon had been achieved, NASA faced funding cuts. Technology and research-based missions weren't seen as important as the landing itself, forcing NASA to cancel some of the planned missions in 1970. As a result, the Apollo 17 mission of 1972 became the last manned mission to the moon.

Firsts and records

Apollo 17 was a 12-day mission that spanned from December 7-19. Apart from the distinction of being the last human expedition to the moon for now, Apollo 17 also achieved a number of firsts and broke some records. It had the then longest space walk and enabled the collection of the largest lunar samples brought back to Earth. It was the first Apollo mission to be launched at night and allowed a scientist to walk on the moon for the first time.

The scientist in question was Harrison H. Schmitt, a geologist who had been part of the backup crew for Apollo 15. Schmitt was originally scheduled to go on Apollo 18, which was cancelled. The scientific community lobbied for Schmitt's inclusion in Apollo 17. While Schmitt served as the pilot of the lunar module "Challenger", Eugene A. Cernan was commander and Ronald E. Evans was the pilot of "America", the command module.

Following a successful night launch on 7, Apollo 17 achieved lunar orbit insertion on December 10. Then, with Evans orbiting the moon, Cernan and Schmitt flew Challenger and landed on the moon's surface on December 11, touching down within 200 m of the targeted landing point.

Two primary objectives

Apollo 17's two primary objectives were to obtain a specific sample and to explore geologically recent, explosive volcanism. The former was achieved as they retrieved the oldest known unshocked (unaltered by meteoric impact) rock from the moon. This sample, called Troctolite 76535, is believed to be at least 4.2 billion years old.

The second objective was met as Schmitt discovered orange soil near Shorty crater. This colour was the result of orange and black volcanic glass that had formed in the type of volcanic eruption that is referred to as "fire fountain" on Earth.

Cernan and Schmitt were on the lunar surface for 75 hours, the longest till now. They clocked 22 hours of extravehicular activity (EVA) with the help of their rover and travelled about 36 km. They went as far as 7.4 km away from the Challenger, close to the limit of what was considered the walk-back distance possible, should the rover have failed. Apart from conducting various experiments, they took over 2,000 photographs and collected 110 kg worth of soil and rock samples from 22 different sites.

Last man on the moon

Following the third and final EVA, the duo televised the unveiling of a plaque with a message, which they left on the moon. On December 14, Cernan took humankind's final step, to date, off the moon.

After lifting off from the moon, the Challenger was docked with America on December 15. Four days later, on December 19, the Apollo 17 capsule splashed down in the Pacific Ocean at a distance of 6.5 km from the recovery ship, after a mission elapsed time of 301 hours.

For 50 years, Cernan has often been referred to as the last man on the moon. With NASA's Artemis program aiming to return to the moon and even set up a sustained human presence, it might not be long before the next human being sets foot on the moon.

Picture Credit : Google 

A protogalaxy is in simpler words a primeval galaxy. It refers to a galaxy that is undergoing the first generation of star formation. It is also defined as a cloud of gas that is forming into a galaxy. This particular celestial mass would just comprise hydrogen gas trapped in some dark matter prior to the initial stages of star formation. The stars are formed from the smaller clumps of gas in the protogalaxy.

Types of Galaxies

 There are two types of galaxies viz. elliptical galaxies and spiral galaxies. The majority of the galaxies that you come across are elliptical galaxies and they are called so because they have an even, ellipsoidal shape. They also are comprised with a greater population of older stars when compared to spiral galaxies.

A spiral galaxy normally has a rotating disc replete with spiral 'arms. The stellar orbits are circular in shape and they have a flattened disk system. Most spiral galaxies also contain in their centre a mini-elliptical galaxy. Our galaxy, the Milky Way, is a spiral galaxy.

So what determines the shape of a galaxy? The rate of star formation during galactic evolution determines whether it turns out into a spiral or elliptical galaxy. If the star formation is at a slower pace, then it turns into a spiral galaxy.

Milky Way

About 12.5 billion years ago, the Milky Way started to form. Several huge clusters of stars and clumps of gas fused together to form a protogalaxy. This was the building basis of our home!

It then collided with many galaxies, and after a lot of mergers, it acquired its present form.

Recently, scientists discovered a population of millions of stars at the center of our galaxy. Those were the remains of the ancient protogalaxy! These oldest stars that were found in the core area of our galaxy were analysed and the scientists found out that they were part of a protogalaxy.

The diameter of which extended to 18 thousand light-years, and with a mass that was 50-200 million times that of the Sun!

Picture Credit : Google 

This new black hole is 1.600 light-years away in the constellation Ophiuchus So far scientists have discovered 20 black holes in the Milky Way. About 100 million more are estimated to be present in our galaxy.

A new black hole has been discovered very near to Earth, closer than any other previously found. Christened Gaia BH1, this dormant blackhole is 1.600 light-years away in the constellation Ophiuchus.

This new black hole is ten times as massive as our sun. To date, scientists have found 20 black holes in the Milky Way galaxy whilst 100 million more are estimated to be present in our galaxy. The newly discovered one is three times closer than the earlier black hole which sat about 3,000 light-years away in the constellation Monoceros.

Since there are more undetected black holes, even this newly discovered one wouldn't hold its spot of "closest to Earth" for too long.

The discovery was mentioned in a paper in the peer-reviewed Monthly Notices of the Royal Astronomical Society. The black hole was discovered by "Kareem El-Badry, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics and his colleagues.

They found evidence of the existence of this dormant black hole using the data from the European Space Agency's GAIA (Global Astrometric Interferometer for Astrophysics) spacecraft. After they noticed a star in the constellation Ophiuchus moving in unexpected ways, they understood that it was a result of the gravity of an unknown, massive object. Using the observation from other telescopes, they confirmed that the object causing this was a black hole.

What is a Black Hole

A black hole is a celestial body that has an immensely huge gravitational pull, so huge that nothing escapes it. Not even light can escape i it!

The black hole grows by accumulating matter that falls in it. Black holes are formed at the end of the life of a big star. When a massive star collapses after its nuclear fuel depletes, it will collapse onto itself and become a black hole.

 It was in 2019 that an image of a black hole was captured for the first time. It was an international collaboration and the astronomers used the Event Horizon Telescope (EHT), networking eight ground-based radio telescopes.

Picture Credit : Google