Individual activity: Mission of Galileo Space Probe to Jupiter

An unmanned spacecraft called Galileo named after the Italian astronomer Galileo Galilei, was sent to study the planet Jupiter and its moons and other planets in the Solar System.

It was launched by the Space Shuttle Atlantis on October 18, 1989. The probe consisted of an orbiter and an entry probe.

Assisted by the gravitational pull of Venus and Earth, Galileo arrived at Jupiter on December 7, 1995, and became the first spacecraft to orbit Jupiter.

The spacecraft then launched the first probe into Jupiter, and was able to directly to measure its atmosphere for the first time.

Even though it suffered some major antenna problems, Galileo studied the asteroid flyby  of 951 Gaspra, and discovered the first asteroid moon, Dactyl, around 243 Ida.

In 1994, Galileo also observed the Comet Shoemaker–Levy 9's collision with Jupiter.

Jupiter's atmospheric composition and ammonia clouds were also studied where it was found the clouds were possibly created by outflows from the lower depths of the atmosphere.

Io's volcanism and plasma interactions with Jupiter's atmosphere were also recorded. The data Galileo gathered supported the theory of a liquid ocean under the icy surface of Europa, and there were evidences of similar liquid-saltwater layers under the surfaces of Ganymede and Callisto.

Ganymede was shown to possess a magnetic field and the spacecraft found new indications for exospheres around Europa, Ganymede, and Callisto.

Galileo also revealed that Jupiter's faint ring system comprises of dust from impacts on the four small inner moons. The extent and structure of Jupiter's magnetosphere was also charted.

After 14 years in space and 8 years in the Jovian system, Galileo's mission was completed by sending it into Jupiter's atmosphere at a speed of over 48 kilometers per second (30 mi/s), eradicating the possibility of contaminating Jupiter’s moons with our terrestrial bacteria. This mission was terminated on September 21, 2003

(This summary of Galileo’s mission to Jupiter was sourced from Wikipedia search)

Solar System forum Planets, Sub-planets, dwarf planets, planetoids. How many actually?

Student Academic Forum on Astronomy

University of Oxford


lim ju boo


Quite frankly since I was a child I knew there were just eights planets, namely the inner ones Mercury, Venus, Earth, and Mars, and the outer giant ones being Jupiter, Saturn, Uranus and Neptune. That was all I knew as a child.

Later they included the most distant and smallest one Pluto discovered by Clyde Tombaugh in 1930 to make it nine. Then when I left school, I read many of them have moons including Charon Pluto’s moon

Then came many rocky objects large and small called the asteroids orbiting between Mars and Jupiter, within a belt called the asteroid belt.

After that I learnt  about the comets, the most famous one called Halley’s Comet originating from the Oort’s Clouds far out from the Solar System,  and other objects in the region of Pluto called the Kuiper belt, as well as many objects some even farther away than Pluto. With all these discoveries they downgraded Pluto and now say Pluto is not a planet but a dwarf planet

Then came other objects called plutinos which they say are trans-Neptunian objects that orbit in 2:3 mean-motion resonance with Neptune. I wonder what that mean?

Now I am wondering which heavenly bodies circulating around the Sun are planets, dwarf planets, sub-planets, planetoids?  Astronomers sometimes reclassify them.  Do they reclassify them according to sizes just like Ceres has been reclassified after the discoveries of more asteroids and other dwarf planets!

Frankly now I have not much idea how many can be called planets, dwarf planets, sub-planets, large asteroids, comets, meteoroids, etc.  I don’t even know how many of these large and small bodies are there actually orbiting the Sun. It looks to me there may be in their thousands just like the asteroids in the asteroid belt. I really don’t know. Maybe Dr. Grant Miller can tell us.  But I still like to stick to my 9 planets in the Solar System, the rest I just like to call them dwarf planets.

I think we  have to leave this problem to the astronomers to tell us exactly how many planets, sub-planets, dwarf planet, planetoids are there circulating around our Sun, and give us  reasons for their classification, whether  they are according to their sizes, mass, composition such as gaseous, icy, rocky…or whatever

Even the number of moons and their names orbiting around most of the planets is quite a mouthful for me to digest, let alone remember their names, composition, properties and characteristics

I only just need to be aware of all these discoveries in this simple course on astronomy which is already quite a bit of new information and quite enjoyable for me to read and discover

Thank you for enlightening me.

Stellar Formation

How did astronomers come to this theory on stellar formation?

by Ju Boo Lim - Saturday, 19 October 2019, 5:54 PM

I read with great interest the formation of young clusters of stars  from collapsing clouds

As the cloud accretes through gravitational forces they form prestellar core, and as  more and more hydrogen (I suppose) collapsed, they form protostars

The hydrogen of these prostar core begins to heat up, fuse, and form stars, and they begin to change hydrogen into helium through nuclear fusion.

The radiation from these newly formed stars began to push materials away from them so that  they become isolated stars

I hope I got this scenario right from the text I read in this course 

I also understand that the formation of clusters of stars from the accretion of surrounding clouds may take tens of thousands of years.

This raises one question I have in mind.

 How did astronomers know this entire event took place  if it takes such a long time for stars to form from the surrounding clouds and dusts?

In Science we can only make a conclusion based on two factors.

First, we make an inference based on a theoretical assumption that relies on already known facts such as gravity can pull matter together, and that matter crushing together can heat up. This is perhaps basic physics.

Second, we can also  base a conclusion by direct observation and measurements

But since what I read in this Unit 5 that it takes some tens of thousands of years for clusters of stars to form, there is no way for present day astronomers, or for any astronomer in the past to be able to  live for such a long time  to observe the entire scenarios to make this conclusion?

I believe even in their entire life span, of  let's say 100 years, and even if they observe the same nebulae night after night for a 100 years, they would still not be able to see any stellar formation within the nebulae or even any changes or movement in the nebulous clouds.  Am I right?

Thus my question is, did astronomers  actually see or have measured the contraction of the prestellar clouds and saw the birth of young stars within their entire  life time?

I am of course not   questioning the hypothesis of stellar formation from what I read here. The theory  can be dead right. After all, I am not an astronomer or an astrophysicist, else I would not be taking this course to learn something..

I am just being curious after what I read in the text,  and I am only asking a question like a student.

Let me give an example.

Take for instance the Crab Nebula in Taurus A (catalogues as  M1, NGC 1952)

We know it is a very bright supernova remnant first recorded by the Chinese astronomer in 1054, and later by the English astronomer John Bevis in 1731.

It lies about kiloparsecs (6,500 ly) away  from Earth and has a diameter of 3.4 parsecs (11 ly) with an apparent diameter of some 7 arcminutes

We know it is expanding at a rate of about 1,500 kilometres per second (930 mi/s), or 0.5% of the speed of light.

I think we can measure that  in our lifetime  for us to conclude that this  nebula is expanding due to a massive supernova explosion, and not contacting into a star.

I guess astronomers can make the measurements of  this expansion within a few years  since stellar distances can easily be measured by parallax method, or if too far away using Cepheid variables by their insintric  variations of luminosity over time.

Further distances like the Crab Nebula, their distances can be measured by the luminosity of their supernova explosions. This they have done within their life time, and hence they can conclude the Crab Nebula is a supernova explosion and is expanding at the rate they have measured.

 So we can conclude the Crab Nebula was a super massive star that exploded tens of thousands of years ago by intra-polating its explosion rate over many years

But how do we measure stellar formation by just measuring the size of nebulae surrounding clusters of young stars

Did the astronomers actually saw it shrinking, collapsing and matter accreating  into stars?

That is my question.  It is so puzzling and fascinating to me

Maybe Dr Grant Miller can help us answer this question

Thanks for reading

Jb lim

Cosmic Scenario before and soon after The Big Bang

I really do not know what exactly the cosmic scenario was before and soon after the Big Bang

If you were to ask me what ingredients I would like to add during those moments, I would first like to ask myself how did that single point in time, space and matter came about if we assume there was completely nothing to start with, not even the presence of just a point of everything, assuming that everything we see or believe was there as we see or can detect them today, example galaxies, black holes, dark matter, energy, gravity... etc. etc.

The question I like to ask myself is how did these ingredients get there even before the Big Bang.

The other question I like to ask is, why was or were they there in the first place, and who put them there  so that the birth of the universe was possible?

I really do not know despite all the theories and assumptions put forward

Once we can answer that, then I suppose putting in the ingredients like sub atomic particles, the charges, gravity, energy whatever the form.. be it heat, microwave radiation, electrical, etc, etc. and then feed them into a computer and ask it to simulate how they would react with one another a tiny nanosecond after the Big Bang and observe the scenario after that should not be a problem

I think at least for me who is not familiar with theoretical physics, we are making assumptions because nobody was there to see or record the events before and after the birth of the universe

I can only read the theories of cosmologists and astrophysicists and maybe just accept them without commenting.

Sorry I cannot comment except ask questions to the mystery

Can a Universe be Reborn from a Super Massive Black Hole?

Can a Universe be Reborn from a Super Massive Black Hole?

by Ju Boo Lim - Tuesday, 29 October 2019, 11:38 am 

Earlier I posted my answer on the Schwarzschild radius for a black hole for the Sun, Earth and Moon asked in this forum discussion

 I gave the answers as:

1.       The Schwarzschild radius for the Sun = 2,954 metres

2.       The Schwarzschild radius for Earth = 8.869513457 x 10-3 metres

3.       The Schwarzschild radius for the Moon 1.0913 x 10 -4 metres .

Then I worked out the Event Horizon radii also for the other two biggest planets in our Solar System, namely, Jupiter and Saturn

Here are the results:

1.       Schwarzschild radius for Saturn 0.844 metres

2.       The Schwarzschild radius for Jupiter 2.82 metres

But I forgot to mention it is not possible for any planet or star except for a neutron star or stars with at least 5 – 10 solar masses to become a black hole when they burn out their nuclear fuel and began to collapse under gravity

What I wrote there and here are just in theory and only for academic interest based on the equation 2Gm/ c2 where G = gravitational constant, m = mass of the star, and c = velocity of light.

But in practice it is neither possible for our own Sun, nor the Earth and Moon to collapse into a black hole because none of them are massive enough.

Even our own middle-age Sun when it runs out of fuel in another 5 billion years’ time, may just bloat up as a giant red star to engulf the Earth, maybe up to Jupiter. It is just not massive enough to become even a neutron star, let alone a black hole.

But suppose all the 250 billion sun-like stars in our own Milky Way Galaxy and the entire Universe were to run out of hydrogen-helium fuel and collapse in theory, what then would the sizes of their black hole?

Here’s the answer I worked out for theoretical academic interest only

1.       The Schwarzschild radius for the Milky Way 1.7133 x 10 15 metres = 181 light year

2.       The Schwarzschild radius of the Universe 8.911 x 1025 metres = 9,419,661,734 light years

Again, this may not be likely as the individual stars masses are different, and their life spans are also different, and it is highly they will not all collapse together at the same time to become  the most massive and biggest black hole in the future 

But what happens if they do? Will their Schwarzschild radius remain the same?

My feeling is, probably the density would be so enormous that even their supermassive black hole itself may squeeze even further to become just one point as if it was in the beginning before the Big Bang.

Is this possible? If this is possible my feeling is that the Universe can begin another episode of the Big Bang, collapse, Bang again like a Pulsating Universe. Is this possible?

I am not saying my “theory” is correct or possible. I am only asking a question out of academic interest

Thanks for reading

jb lim

Malaysia

The Collapse of the Stars

The End of Stars Forum Discussion

One of the questions I asked during our academic forum discussions on “The End of Stars” was this question

How was that when the critical Chandrasekhar mass limit is reached, the electrons can no longer resist each other and gravity overcomes their electromagnetic repulsion? 

When that happens the white dwarf can no longer be supported and the core collapses further, fusing electrons and protons into neutrons now held up by the mutual repulsion of neutrons to become a neutron star.

My question is how was that gravity which I thought is the weakest of all forces has now become the strongest overpowering even nuclear forces that kept protons and electrons apart.

The best guess I can give is that the mass of the star must be been so enormous, maybe 3 or more solar masses that the product of their masses is so colossal that they overwhelmed the nuclear forces that kept the protons and electrons apart.

I am unsure as I am not a physicist let alone a nuclear physicist. I am just learning fascinating facts in this interesting course.

I really hope Dr. Grant PhD (Astrophysics) can explain to clarify

In Search of Extra Terrestrial Civilization: Flaws in Frank Drake Equation

When I was doing my continuing education course in astronomy from the University of Oxford late this year (2019), we have to have to participitate in countless academic and forum discussions almost everyday before we could complete the course

In one Unit of the couse was one on Astrobiology where under this sub-unit was one on Frank Drake equation. I shall reproduce below this sub-unit:


8.6 The Drake equation


"One of the early advocates of SETI, Frank Drake, created an equation which helps you estimate the number of communicating civilizations in the galaxy. To make an estimate you need to know a large number of unknown values – so essentially the equation is structured guesswork. As we learn more about exoplanets and about life, we are able to narrow down some of the numbers, and the equation gives you a feel for how likely you are to ever communicate with aliens.


The equation gives you N, the number of communicating civilisations in the galaxy:

N = R * fp * ne * fl * fi *fc * L,

where R is the average rate of star formation in our galaxy; fp is the fraction of stars with planets; ne is the number of Earth-like planets per Solar System; fl is the fraction of those which evolve life; fi is the fraction of those that evolve intelligent life; fc is the fraction of intelligent lifeforms that develop technology for communicating with aliens; L is the lifetime of a communicating civilisation, in years.


We currently believe that R is approximately 7 stars per year. We are getting more and more data on fp and ne all the time. Whilst fl may be a small fraction, fi and fc may not be, if we think intelligence and communication are consequences of evolution. L is very hard to guess, since we are the best and only example of a communicating civilisation, and we’ve been communicating for less than 100 years!


In 1961, Drake and his colleagues came up with the following estimates for the numbers:

N = 1 * 0.25 to 0.5 * 1 to 5 * 1 * 1 * 0.1 to 0.2 * 1000 to 100,000,000 This gave Drake a value of N in the range 1000 to 100,000,000 communicating civilisations in the Milky Way."
(Source: University of Oxford)

Below was what I replied for the forum discussion

 I am amazed how did Frank Drake come up with his equation when there is no data to work on to substitute into his equation. 

The only world so far we know that has life on it is on this planet Earth of ours. None of the planets, dwarf planets or any other body in our own Solar System has any. So are the many and increasing numbers of exo-planets in other stellar systems being discovered has any.

In the absence on the data of life existence, how is it possible for anyone put some theoretical numbers on his equation to predict the numbers of life as we know it, let alone civilization, or even intelligent civilizations in existence in our Milky Way Galaxy?

At the moment  we just have one point (Earth) to work on. We can’t do very much with just one point or a single data. We don’t even have another number to join two points together to extrapolate anything further.


Whatever cooked-up data we like to substitute into Frank Drake equation, it would  just be guesswork and theoretical. This is just not scientifically real


We can of course put any numbers we like. That’s not a problem, but are they real numbers? Is that statistically correct? In statistics if we want to draw a scientific conclusion we must have as large a population as possible, the larger the numbers, the better to represent a true population.


Maybe we have some idea on R which is the average rate of star formation in our galaxy as discussed in Unit 5, and fp as the fraction of stars with planets (based on the numbers of extra solar planets we have discovered so far as argued in Unit 6).


 Maybe we can even extend the equation to “ne” as is the number of Earth-like planets per Solar System based on habitable planet as discussed in 6.8 on The Goldilocks Zone.


But to go further than that, further away into the equation is a bit difficult. Even if we imagine the closest possibility we can use to substitute into the initial part of the equation, it would just be intelligent guesswork, let alone put in some theoretical or imaginary data into the full equation
We may come out with a result which may be far out from statistical reality on facts and figures
I cannot imagine how Drake and his colleagues in 1961 came up with the following estimates for the numbers as:


N = 1 * 0.25 to 0.5 * 1 to 5 * 1 * 1 * 0.1 to 0.2 * 1000 to 100,000,000 communicating civilisations in the Milky Way?


Even SETI programme with all their arrays of radio telescopes and world-wide citizen search has not shown up any intelligent life this far. 


However, this does not mean there is no other life in this horrendously immense Milky Way Galaxy of ours, let alone in the entire Observable Universe.


Stand Alone World:

For us to believe we are the only world that harbours life on it, is like us standing on a vast, vast seashore of sand, and saying beneath our feet there is only one, and only grain of sand, on which surface teems tiny microbes, while all the other grains of sands as far as our eyes can see over and across the horizon are all sterile


Is that what we believe? Is that a statistically probability? We will be extremely arrogant and haughty to believe this.


What I express here in this forum is just my personal view.