The Milky Way is Really Big

The Milky Way Galaxy (the one we’re in) contains an estimated 200 billion stars. But that’s just the tip of the iceberg, the Galaxy is surrounded by vast amounts of an unknown material called “dark matter” (matter that we can’t normally detect because it doesn’t interact with the electromagnetic spectrum). Astronomers know it exists because, dynamically, the Milky Way would fly apart if dark matter didn’t keep a gravitational lid on things.

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Still, astronomers would like to have a more precise measure of the Galaxy’s total mass to better understand how the myriad galaxies throughout the Universe form and evolve. A team of researchers from ESO, the Space Telescope Science Institute, the Johns Hopkins University Center for Astrophysical Sciences, and the University of Cambridge combined observations from the NASA/ESA Hubble Space Telescope and ESA’s Gaia satellite to study the motions of globular star clusters that orbit our Galaxy. The faster the clusters move under the entire Galaxy’s gravitational pull, the more massive it is. The team concluded the Milky Way has an equivalent mass of 1.54 trillion solar masses, most of it locked up in dark matter.

This new mass estimate puts the Milky Way Galaxy on the beefier side, compared to other galaxies in the Universe. The lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion, or 30,000 times more massive. The Milky Way’s mass of 1.5 trillion solar masses is fairly normal for a galaxy of its brightness.

Previous estimates of the Milky Way’s mass ranged from 500 billion to 3 trillion solar masses. This huge margin of error arose primarily from the different methods used for measuring the distribution of dark matter, which makes up about 90% of the mass of the Galaxy.

Given the elusive nature of the dark matter, the team had to use a clever method to weigh the Milky Way, which relied on measuring the velocities of globular clusters, dense star clusters that orbit the spiral disk of the Galaxy at great distances.

The scientists used Gaia’s second data release, which includes measurements of globular clusters as far as 65,000 light-years from Earth, as a basis for the study.

Observations from Hubble allowed faint and distant globular clusters, as far as 130,000 light-years from Earth, to be added to the study. As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.

By combining Gaia’s measurements with measurements from Hubble, the scientists could better pin down the Milky Way’s mass in a way that would be impossible without both space telescopes,

The team’s results will be published in the Astrophysical Journal.

Old Scars on Mars

Mars is a cold, dry place, but it may not always have been. Recent studies increasingly indicate that the planet once had a thicker, denser atmosphere that was able to lock in far more warmth, and therefore facilitate and support the flow of liquid water on the surface.

While this is no longer the case, planetary researchers have seen clear signs of past water activity across the Martian surface. New images from ESA’s Mars Express orbiter show one such region: a branching system of trenches and valleys in the southern highlands of Mars.

The southern highlands are some of the oldest and most heavily cratered parts of the planet, with many signs of ancient water. The topography of this region suggests that water flowed downhill from the north to the south, carving out valleys up to 1.2 miles (2 km) across and 656 feet (200 m) deep as it did so.

It is thought that climate change took place on Mars 3.7 to 3.8 billion years ago, when environmental conditions changed from a somewhat neutral, potentially life-sustaining and humid environment to a much drier, colder environment that is hostile to life.

One of the reasons why Mars lost its atmosphere was the loss of its magnetic field, which was active during its first 500 million years.

As the magnetic field grew weaker the solar wind was able to gradually split the molecules in the atmosphere. The resultant ions were then lost to space. As a result, and also due to declining volcanism, the atmosphere became thinner. Below a certain atmospheric pressure, water can no longer remain liquid on the surface of a planet, it can only remain as ice or gas.

Mars is also only about half the mass of Earth, so its gravitational force is barely sufficient to bind atmospheric molecules to it and the lack of precipitation on Mars collapsed the water cycle.

While it is unclear where all of this water came from originally (precipitation, groundwater, melting glaciers) all of this required a far warmer and more watery past for Mars.

Philae Back From the Dead

The comet lander Philae has awakened from a seven-month hibernation and managed to communicate with Earth for more than a minute, the European Space Agency (ESA) said Sunday.

The probe became the first spacecraft to land on a comet when it touched down on the icy surface of 67P/Churyumov-Gerasimenko last November. Shortly after its historic landing, Philae managed to conduct several experiments and send data to Earth for about 60 hours before its batteries depleted and it was forced into hibernation.

The German Aerospace Center, which operates Philae, said that the probe resumed communication at 10:28 p.m. (2028 GMT; 4:28 p.m. EDT) on Saturday, sending about 300 packages of data to Earth via its mother ship Rosetta, which is orbiting the comet.

There’s a Philae Comet Alien Conspiracy Theory, Because of Course There Is

As with everything from the moon landing to the death of Elvis, an alternative version of “what really happened” as the Philae probe landed on comet 67P did not take long to emerge.

According to an email published on the website, which does a regular trade in alien sightings, the mission was part of a European Space Agency and Nasa cover-up to disguise the comet’s true alien nature. The email, allegedly from a secret whistle-blowing employee of the ESA, accuses the agency of “blatant cover-ups” in wanting to land on the speeding comet and attaches photos which claim to reveal the “true inner workings of Comet 67P”.

It states:

Do not think for ONE MOMENT that a space agency would suddenly decide to spend billions of dollars to build and send a spacecraft on a 12-year journey to simply take some close-up images of a randomly picked out comet floating in space.

Some 20 years ago Nasa began detecting radio bursts from an unknown origin out in space. It would later be known that these had likely come from the direction of the now named comet 67P. It does show signs on its outside of machine like parts and unnatural terrain.

Ending on an ominous note, the letter adds: “Whatever this object is, it did not ask to be found or scrutinised.” (cue dramatic music sting)

This is far from the only extra-terrestrial conspiracy theory put forward about 67P and the ESA mission. In September, BPEarthWatch published a video showing “brand new, hi-res” images. Taken from the Rosetta spacecraft, they appeared to show two UFOs flying over the comet and a transmission tower-like structure built on the surface, potentially emitting the mysterious radio signals which have been picked by the ESA. “These images are not normal,” says the video voiceover.

The ESA’s confirmation that the comet had been emitting a “mystery song” has fuelled theories that it is in fact an alien ship and the warbling is an extra-terrestrial attempt at communication.

Goodnight, Sweet Prince

The batteries aboard the European Space Agency’s Philae comet lander drained Saturday, shutting down the washing machine-sized probe after an adventurous and largely unscripted 57-hour mission.

Photos and other data relayed by Philae show it landed against a cliff or crater wall where there was little sunlight to recharge its batteries. Racing against the clock, scientists activated a series of automated experiments, the first to be conducted from the surface of a comet.

Before dying, Philae defied the odds and radioed its results back to Earth for analysis.

Its last task was to re-position itself so that as the comet soars toward the sun, Philae’s batteries may recharge enough for a follow-on mission. Scientists are particularly interested in learning about the chemical composition of any organic molecules in samples drilled out from the comet’s body.

Comets are believed to be pristine remnants from the formation of our solar system some 4.6 billion years ago. They contain rock and ice that have preserved ancient organic molecules like a time capsule and may provide insight into how the planets and life evolved.

Rosetta in August became the first spacecraft to put itself into orbit around a comet and it will accompany the comet as it travels toward the sun for at least another 13 months.