Did Galileo discover Neptune?

We all know that the farthest planet in the solar system, Neptune was discovered in 1846. French astronomer Johan Galle observed it first by using mathematical predictions in celestial mechanics done by French mathematician Urbain Le Verrier. As British mathematician, John Couch Adams also invented mathematical predictions there became a dispute over the credit of discovery. Ultimately the honor was shared.

History says that Johan Galle detected Neptune as the first time in the history of astronomy on September 23, 1846. But did you ever wonder whether any one might have at least seen it through a telescope before that day?

The answer is yes. But when and how? Neptune is even impossible to see in naked eye. Therefore even locating it in the night sky to focus a telescope is also impossible. So it must be accidental. Yes you thought right.

Our famous astronomer Galileo Galilei was very keen on observing Jupiter and its four moons discovered by him Also Jupiter was one of his favorite in the night sky. He observed a faint blue star very near to Jupiter at morning sky on December 28, 1612. Also he observed this faint blue star again just after a month at morning sky on January 27, 1613.  We know this because he took notes about these observations and it has been nearly two decades since the world have come to known about this.

Astronomers by calculations and computer simulations have found that this blue star is actually Neptune which was in conjunction with Jupiter at that time. Neptune was in a backward motion relative to earth as it had just turned retrograde motion in December 1612. It has been long speculated by astronomers that Galileo observed Neptune but he didn’t recognized it as a planet.

Do you want to see for yourself that how the sky looked like when he observed it? You don’t need to know any sort of mathematics. You just need the freeware Stellarium. Download and install it in your computer. Just set the location to Earth, Pisa and set the time to December 28, 1612. See the morning sky for yourself at about 7 AM. Bingo!! Here’s my view. I took some screenshots for you to see.

Do the same for January 27, 1613. Here are my screenshots.

In both cases you could see Neptune near Jupiter. COOL!! Isn’t it?

In July 2009 University of Melbourne physicist David Jamieson announced with evidence suggesting that Galileo was at least aware that the star he had observed had moved relative to the fixed stars.  He says that Galileo had marked the position of Neptune which he had observed on January 6 as a black dot on the notebook of his observation on January 28 1613.This black dot has been discovered as the precise position of Neptune on that day. Then he believes that as the object had moved relative to a star nearby Galileo might have thought that he had actually discovered a planet. Jamieson even decided to do a chemical analysis of the trace elements on the page of observation notes, intending to find whether he marked the January 6 observation on January 28.

So what do you think? I think that Galileo just missed his chance for being credited as the discoverer of planet Neptune.

Mercury has water-ice!!!

Mercury

The Mariner 10 space probe made three passes by the planet Mercury in 1974 and 1975. But it could only explore 45 percent of the planet surface. Therefore Scientists continued ground observations of planet Mercury.

In 1991, planetary scientists Duane Muhleman and Bryan Butler from Caltech and martin Slade from the Jet Propulsion Laboratory decided to study Mercury by radar. What they did was that they sent a beam of 8.5 GHz, 460 kW microwaves  from a half-million watt power transmitter radar system in a 70-meter dish antenna at NASA Deep Space Network , Goldstone, California targeting Mercury.  The radar waves reflected from Mercury were received by the National Radio Observatories 26 VLA (Very Large Array) antennas. Then scientists filtered and processed the returned waves and produced a map of Mercury according to the radar reflectivity of its surface .This the map they got.

Radar image in 1991

In this radar image red indicates strong reflection and yellow, green and blue progressively weaker reflection. You can see a bright red spot at the Mercury’s north pole. In 1994, the same observing team discovered similar reflection’s from the Mercury’s south pole.

Then in 1999, astronomer John Harmon at the Arecibo Observatory in Puerto Rico repeated the 1991 study. This time he used a more powerful beam of microwaves emitted by the Arecibo Radio telescope and the reflected waves were detected by the VLA radio telescope array in New Mexico. This is one of the high resolution images of Mercury’s North Pole that was made by using the data of reflected waves.

Radar image made in 1999

Scientists were surprised to see these reflections from Mercury. Their deduction was that such kind of strong reflections can never be made from a momentary “glint” off a crater wall. When studied further these characteristics of reflections were similar to the ones from the water ice on Mars and icy moons of Jupiter. Although water ice found on earth absorbs radio waves, ice at very low temperatures is a very effective reflector of radio waves. So you know what I mean. Can there be ice on the surface of such a scorching hell like Mercury? Well, scientists say why not?

We all know that Mercury is the smallest planet in the solar system and also the closest to the sun. Being so small to retain an atmosphere its surface temperature varies horribly. Therefore its day side is hot as frying 427 degrees Celsius where as its night is frigid minus 173 degrees Celsius. As the axial tilt of Mercury is nearly two degrees, some crater floors in the poles of the Mercury are in constant shade and never get sunlight, resulting a temperature below minus 170 degrees Celsius. With no atmosphere to trap heat these areas can trap cold and called as “cold traps”.   Debris or vapor drifting from interplanetary space could be permanently captured in cold traps as ever deepening rimes of frost.  

Scientists propose that meteorites in the past potentially carried large amounts of water to Mercury’s surface. Also outgassing of water from the planet’s interior could also provide a non-negligible flux of water to the surface. If any water found its way to the cold traps it would freeze and remain. Also it has been revealed that there should be several meters or more thick  at least 90 percent pure ice to give such strong reflections, indicating that each deposit was laid down in one or a small number of rapid events, such as a large comet impact.   Scientists say that to remain the ice stable there should be a thin (10-20 cm) layer of regolith (layer of dust, soil and broken rock)on them.

Considering the bright radar spots to be frozen ice deposits scientists have calculated that there could be 10¹⁴ to 10¹⁵ kg of ice. I would give a data to compare this. The Antarctic ice sheet here in the earth has a mass of about 4 x 10¹⁸ kg. That really is lot of water. Isn’t it?

   

The MESSENGER space probe, only one to visit after Mariner 10 reached the Mercury in March 2011. It created a global map of Mercury by sending back 87,000 images within its first year. Scientists examined the topographical data and created a 3D model of Mercury’s poles. Here, they could discover cold traps with permanent shade. Also by processing images in the poles they could produce the illumination maps which are given below.

An illumination map of Mercury's south pole(left), black areas are cold traps.The respective visual image(right)
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institute of Washington  

The researchers superimposed observations of radar bright patches by the Arecibo Observatory on the latest photos of Mercury's poles taken by the MDIS imaging instrument aboard Messenger.Stunningly, the areas with constant shade or cold traps perfectly matched the radar bright spots, supporting the water-ice hypothesis. But this evidence does not confirm that there is water ice. Because, sulfur has also been proposed as the cause of radar-bright spots. Therefore in order to affirm the composition of cold traps, looking for hydrogen on Mercury by examining neutrons was done by MESSENGER’s neutron spectrometer.  

Top:Mercury's north pole in visible light, Credit: NASA/JHUAPL/CIW
Bottom: Same place in Radar image, Credit: NAIC/Arecibo

Two images superimposed, yellow patches are bright radar spots,Credit:NASA

Neutrons are created when cosmic rays hit Mercury. They break atoms into their component particles. Scientists can determine the abundance of hydrogen on Mercury by mapping the relative flux of neutrons at different energy levels. Hydrogen in Mercury’s soil would slow down the particles, making them less energetic. As the most likely source of hydrogen in the solar system is water this is an interesting experiment. Currently, Scientists are still crunching the numbers of received data.

Finally we can hope that discovery and confirmation of water-ice on Mercury’s poles would be a great potential for human colonization on planet Mercury in future.