You see, even if an explanation lacks, you can observe that it is indeed so.
However, a near radial path to the outer parts of the Solar System, is still possible.
So, you can study the various trajectories of probes, to Venus, Mars, Jupiter etc..,
which are all rather curved. However, once passed, and far from the large Planets,
a radially outward trajectory can be "pretty straight".
Classical mechanics can explain it. See the figure below. When a probe (small red ball),
comes near a large mass (like a planet), the force of gravity, will "arc" (or bend) the path of the probe.
Figure 1.
Remark (2).
It makes a bit of a difference, to "what" you are referring your speed to.
For example: with respect to the Sun? Or, with respect to the Planet?
There are subtle differences here.
Ofcourse, the Sun has a motion in our Galaxy, so the Solar system as a whole, does.
But, you can treat the Sun as a "fixed location", and take a look at the objects
as they move in the Solar system (like an orbit around the sun, or a probe travelling to a Planet).
Remark (3).
Often, probes use a "sling shot" maneuver, or also called "gravity assist",
to use the gravity of a Planet on approach, to alter the trajectory and speed of the probe.
This is often used to visit the outer Planets. But can be used with inner Planets as well.
For example, a probe, on its way to a rather close encounter with Jupiter, can have
altered it's speed and path, for example, in order to get an economic route to Saturn.
However, if you want to use such a "gravity assist", you must take account of certain
suitable lauchdates, because Jupiter and Saturn must have (more or less) the right positions
in their orbits, otherwise your probe arrives too soon, or too late.
Statements (2) and (3) are relatively easy to explain.
To illustrate (3), as often, Wikipedia provides us with great illustrations.
Please take a look at the url below:
Animation of Voyager 1 to Jupiter and Saturn.
=>In a reference frame, where the Planet is at rest:
From the Planet's perspective, the probe gets nearer and nearer, takes a curved path, and moves away again.
In this case, the magnitude of the velocity, Vbefore of the probe, is the same as Vafter,
when the probe is moving away again. Only the direction has changed.
This is from the Planet's perspective, as if it's in "rest".
In this case, the total momentum of the system, is constant. Since the Planet does not "move", the probe
keeps the same speed.
=>From the Sun as reference frame, where the Planet moving in orbit:
From the perspective of the Sun, it's different. The Planet moves, and a probe approaches that Planet.
The total momentum is again, constant. But the Planet "looses" momentum (unmeasurable since the mass is so large),
in favor for the probe, which gains that amount of momentum. You can see that in the vector addition
in figure 1, below. The magnitude of the velocity, the speed (black line), is larger than before.
Figure 2.
In this case, |R2| > |R1|.
If the probe (in general), would have an incoming direction "more from the left", it looses some momentum (speed).
Thus, using "sling shots", a probe may gain or loose speed, and changes direction.
Remark (4).
In note 2 (about the Solar System), the orbital speeds of the Planets are listed in a table.
Take a look at that table again.
Do you see that an outer Planet like Neptune, has an orbital speed of 5.4 km/s, while Earth goes
with a speed of 29 km/s.
If you want to go to the outer planets, you need to lower your orbital speed.
Now, if you send a probe "outwards", it slowly travels through the Sun's gravitational "well".
It's like throwing a stone to a large height, here on Earth. It slows down while travelling upwards.
This happens with your probe too !
Take a look again at the link of the animation above. Watch the animation with attention.
Do you notice that Voyager 1 speed is listed too (bottom-left)? While flying to Jupiter, it looses speed.
Ok, we now have a better idea of trajectories, and let's go to the missions !
Chapter 2. (Subset of the) Missions to Venus.
2.1 Some parameters of Planet Venus:
Distance to Sun: 0.72 AUMass: 0.81 Mass of Earth
Orbital period: 224.7 days
Avg. Orbital speed: 35 km/s
Inclination: about 3.4 degrees to ecliptic
Gravity on Surface: 0.9 g (0.9 of Earth's gravity on surface)
Pressure at surface: 92 atmosphere
Surface temperature: 464C / 867F / 737K
During the '60's up to 2010, about 40 missions in total were done, however, especially in the '60's,
quite a lot failed (e.g. launch failure).
Most successes in '70s, '80s, were achieved by the Sovjet Union.
Especially, the "Venera probes" 8, 9, 10, 13, 14 were very succesful.
Let's first see what happened during the '70s and early '80s, before going to later missions.
2.2 The Russian Venera probes (especially 8,9,10,13,14 in the '70s, '80s):
In 1972, the Venera 8, was the first lander, which touched down on a real planet,for the very first time.
In 1975, Venera's 9 and 10 became the first landers, which also produced images of the
surface, while taking all sorts of measurements as well.
Venera 11, landed succesfully too, but the camera's failed. However, the mission was
succesful in taking other measurements.
The conditions on Venus, are "harsh" to say the least, with a surface temperature around
460 degrees Celcius, and an atmospheric pressure of about 92 bar.
It's a very hostile environment for even an "hardened" probes (as they indeed were).
Typically, a probe could last for a max of about 1 hour.
The planet has a very dense atmosphere, and many scientist call Venus a "run-away greenhouse" planet.
First, take a look at a few of those picures in the links below, and be amazed.
It's so fantastic to see the first pictures of this Planet.
I collected a few links, whichs shows the original photo's, and digitally processed ones.
For the processed ones, often small gaps were reconstructed, and occasionally perspective was added.
However, all objects are "real". It's important to have made that last remark.
Some photo's with additional colours, used Venera 13 data. However all added colourization
might be debatable.
The American researchers Don P. Mitchell and Ted Stryk are known for their work on further processing
the images from Venera 9-14 (but especially 13 and 14), using the original data.
Venera 9 picture, processed photo.
Venera 10 picture, processed photo.
Venera 13, processed photo.
Venera 13 original, partial area.
Venera 9 picture original, and processed.
Venera 10 picture original, and processed.
Venera 14 processed photo.
- In the period '60's, '70's, the Mariners 2, 5, 10 performed succesful flyby's.
- Launched in 1978, "Pioneer Venus 1" entered orbit, and performed a large array of measurements,
among which were creating radar images. - Also launched in 1978, "Pioneer Venus 2" entered orbit, and submitted three probes for decend
in the atmosphere, for a large array of measurements. It was not planned to have a soft landing. - Launched in 1984, the two Russian Vega 1 and Vega 2, performed succesful landings (partly in decent
using a balloon), for large array of measurements. Unfortunately, no camera images exists.
2.3 The US Magellan spacecraft, launched in 1989.
Released from the cargo bay of the Space Shuttle "Atlantis", shortly afterwards,"Magellan" was on it's way to Venus, where it arrived in August 10, 1990.
Main mission: Collecting High resolution radar images, at least covering 70% of the Surface.
The RDRS radar system, ultimately scanned 83.7 percent of the Planet's surface.
What already was hinted by the Venera probes, and the early Mariner scans, was confirmed,
and shown in much more detail, by Magellan.
More than 75% of the surface of Venus, consists of lowland lava plains.
Many Vulcano's are present, some having rather unusual shapes, such as the “pancake domes”.
At places, complex patterns of ridges and cracks can be seen, pointing to tectonic activities.
2.4 The ESA "Venus Express", launched in 2005.
This probe from the European Space Agency (ESA), entered it's polar orbitin april/may, 2006. It's focus wason the study of atmospheric dynamics, and thermal aspects,
in the broadest sense possible.
The collecting of data took place over a considerable amount of time, up to 2015.
It found clues pointing to:
-Amazingly, It found evidence for past oceans.
-It confirms the presence of lightning on Venus and that it is more common on Venus then on Earth.
-There occasionally exists a rather large vortex in the atmosphere, at the South Pole.
-In higher layers of the atmosphere, strong winds may occur, while at the surface,
winds are rather calm.
For about the past oceans, that would indeed be highly remarkable.
The link below shows some more information (nature.com):
European mission reports from Venus (nature.com)
Another nice article on Venus, is this one (nature.com):
Space and astronomy: The girl next door (nature.com)
2.5 Venus, the most Earth-like Planet in our Solar system. What happened?
Below, some great links are listed, describing environmental issues and questionswhich exists around Venus.
Understanding why our most Earth-like neighboor is so different (arxiv).
Document, also describing Venus's evolution (arxiv).
The geology of Venus.
Considering some modern articles about the environment and conditions in the past,
a picture seems to emerge by some Planetary experts, where Venus once was a "close to"
habitable Planet (?), with water, and due to some still unknown factors, a very strong
run-away climate crisis occurred. Indeed. What happened?
I will not say that there exists a consensus in the scientific community on such a view,
but it certainly is most intriguing.
Nice thoughts:
Using balloons seems to be very well possible, in Venus's atmosphere.
Looking at available data, then, for example, at 55 km altitude, we have a reasonably calm atmosphere,
at about 20 degrees Celcius, and a pressure of about 0.5 atmosphere.
The Russian "Vega" missions already proved that a balloon works. They used it partially
in their decends. When the balloon was open, the probes drifted for a long way.
Already some studies by NASA have been done, looking at the feasibility of such plan,
thus using balloons to "sail" over Venus, possibly even in a manned mission.
How about that ! Well..., somewhere in the future, maybe.
You may like to further Google on "HAVOC", which the following Wikipedia page, explains:
havoc (wikipedia)
Chapter 3. Missions to Pluto.
3.1 Some parameters of Pluto:
Distance to Sun: Aphelion: 49.305 AU, Perihelion: 29.658 AU (high eccentricity).Average distance: 39.48 AU.
Mass: 0.00218 Mass of Earth
Orbital period: 248 years
Avg. Orbital speed: 4.74 km/s
Inclination: about 17.16 degrees to ecliptic
Gravity on Surface: 0.083 g (0.083 of Earth's gravity on surface)
Pressure at surface: about 1 Pa (9.8 * 10-6 atmosphere)
Surface temperature: Often referred to as 24K to 38K/-247C to -233C)
Discussing missions to Pluto, just after a chapter on Venus, is quite a step.
From a close neighboor Planet, to a dwarf planet (near, or in, the Kuiper Belt).
While there have been quite a number of missions to the other Planets, like Venus, Mars,
or the outer planets, the number of actual missions to Pluto is.... "1". Yes, just one.
For example, the number of missions to Venus, or to Mars, is well over 40.
This one mission to Pluto, was done with a sophisticated probe called "New Horizons".
A trip to Pluto is very challenging. It's an enormous distance to start with.
Ofcourse, if you want to benefit of a "gravity assist" of e.g. Jupiter, you have to wait
for the moment where the positions of the Planets (Jupiter, Pluto) are exactly right.
That leaves you with a rather narrow window of suitable launchdates.
A redefinition in 2006, at the 26th General Assembly of the International Astronomical Union (IAU),
caused Pluto to be "demoted" from being a full-member(the 9th planet) of the Solar System.
Since then, it has become known as a “Dwarf Planet", or "Kuiper Belt Object (KBO)", and
sometimes also a the "Trans Neptunian Objects" (TNO).
3.2 Illustrations and some facts on the Kuiper Belt.
The Kuiper Belt is a region between 30 AU, up to about 50 AU. So, the inner edge is close to Neptune.It's a sort of a donut shaped region. The residents are mainly composite objects, resembling smaller astroids,
but this time mainly composed of methane, waterice, and some other composites.
But, also a number of dwarf planets have been discovered. The most important ones are Pluto, Haumea and Makemake.
Ofcourse Pluto was already known for quite some time, but today it's reckognized as to be
a member of the Kuiper Belt.
Note how wide the Kuiper Belt is. Neptune is about 30 AU away from the Sun, and the Kuiper Belt,
starts from about 30 AU, up to about 50 AU.
Some nice illustrations of the Kuiper Belt:
Kuiper belt (universetoday.com)
Kuiper belt (solarsystem.nasa.gov) (1)
Kuiper belt (solarsystem.nasa.gov) (2)
Note that in the third link above, also the trajectories of Voyagers 1 and 2, and the Pioneers 10 and 11
are illustrated. However, none of them came close to Pluto.
All of them have "left" the "classical" limit of the Solar System, that is, crossed the orbit of Pluto.
However, we know that the Solar System is quite a bit larger, since we have the Kuiper Belt, and we certainly
must not forget the Oort cloud.
Huh??! Albert..., check your numbers!! Around this date (may 2020), Voyager 1 is close to 149 AU from Earth,
so indeed far beyond the Kuiper Belt. It also crossed the socalled heliosphere.
Voyager 2 is not far from such insane distance as well.
To say that Voyager 1 is now in Interstellar Space, is indeed OK (but it did not crossed the Oort cloud yet).
By the way, later in this note we will see the Pioneers and Voyagers again.
3.3 Illustrations and some facts on Pluto's moons.
There are five moons. However, up to 2005, only "Charon" was a known companion.Charon is indeed a rather substantial moon, since it's diameter is about 1200 km.
Late in 2005, a closer inspection of Hubble footage, revealed two more, small, moons,
which were named "Nix" and "Hydra". They are estimated to have a diameter
of around 50 km (somewhere between 30km and 150km).
Again, using Hubble images, around 2011, two additional moons were found,
"Kerberos" and "Styx", with a size probably no more than 20km.
Relative sizes and positions of the companions of Pluto:
Pluto's 5 Moons Explained: how they measure up (space.com).
Positions of the moons of Pluto during the New Horizons flyby (planetary.org).
During New Horizons flyby, Charon was closely examined too.
3.4 The "New Horizons" mission.
=>The first probe ever, to Pluto.-It turned out to be a very close encounter with Pluto (just 12500 km or 7800 miles, above the surface).
-Later, there was a absolutely fantastic close encounter with a Kuiper Belt object too.
This was the remarkably shaped object 2014 MU69 (or Arrokoth, as it is named today).
=>Mission at a glance:
- Launch Vehicle: Lockheed Martin Atlas V.
- Launch date: January 19, 2006.
- Gravity assist (sling shot) by Jupiter, February 28, 2007.
- New Horizons was put in hibernation, as of June 28, 2007.
- The probe crosses Neptune's orbit, on August 25, 2014.
- New Horizons awakes from hibernation, on December, 2014.
- Pluto flyby: july 14, 2015 (12500 km or 7800 miles above the surface of Pluto).
- Detector Alice on New Horizons, confirmed the existence of a "hydrogen wall" on August, 2018.
- Flyby at dwarf object Arrokoth (or "2014 MU69", nicknamed "Ultima Thule"), on Januari, 2019.
- It might be true, that New Horizons mission may even extend up to 2030.
=> Several position diagrams of New Horizon in the Solar System, near Pluto.
Where is New Horizons now? (jhuapl.edu).
Position of New Horizons at December, 2018.
=> The spacecraft:
The probe, and it's instruments (1).
The probe, and it's instruments (2).
3.5 The Close encounters with Pluto, Charon, and Arrokoth.
Often, a number of probes launched at large time intervals, will have the effect, that the knowledgeof a Planet (or other object), accumulates. That is, it all adds up to a still better understanding.
With New Horizons, it's really a bit different. Before, the knowledge about Pluto, was really slim.
During the flyby, a large amount of data was collected, resulting in a good fundament
of knowledge about this dwarf planet.
=> Images:
First, some absolutely stunning (real) photo's:
Pluto:
Pluto: Whole Planet (1).
Charon:
Charon: Whole moon (1).
Arrokoth / 2014 MU69:
Arrokoth / 2014 MU69 (1).
New Horizons Arrokoth (2014 MU69) Approach.
=> Discoveries:
As said before, the knowledge of Pluto, and Kuiper Belt, was rather thin, and New Horizons cranked
it up significantly.
You can search for the discoveries done by New Horizons.
It's probably best to list some sites discussing this topic, by the experts who can best
interpret the results.
Here, I only like to make a few remarks on what New Horizons found at the flyby with Arrokoth.
Findings on Pluto:
If you like information on the findings, Please visit:
Top New Horizons Findings Reported in Science (nasa.gov)
The Pluto system: Initial results from its exploration by New Horizons (arxiv)
Arrokoth:
Arrokoth, a "Cold Classical Kuiper Belt Object", is a "prestine" object, representing
an object from the earliest phases of the Solar System.
Larger objects, are likely to have formed, by from pebbles aggregation.
Arrokoth has two large spherical components, which seems to have been welded together.
It has a remarkable "peanut" like shape (bi-lobate shape).
The bi-lobate shape points to a contact binary, which took place, likely 4.5 Giga years ago.
It must have been a gentle merger (low speed), otherwise a violent collision would never have created
this rather peculiar shape.
Rather complex Carbon based molecules are likely to have been detected.
It looks like that Arrokoth is covered with "tholins" which stands for a wide variety of organic compounds
formed by e.g. solar ultraviolet or cosmic rays, from more basic compounds as Carbondioxide, Methane, Ethane.
It often shows as a reddish sort of dust, on cosmic objects like Arrokoth.
While tholins are not new, it is a surprise to find it on Kuiper Belt object.
Next, let's go to Mars...
Chapter 4. (Subset of the) Missions to Mars.
4.1 Some parameters of Planet Mars:
Distance to Sun: about 1.5 AUMass: 0.107 Mass of Earth
Orbital period: 687 days
Avg. Orbital speed: 24.1 km/s
Inclination: about 1.50 degrees to ecliptic
Gravity on Surface: 0.381 g (0.381 of Earth's gravity on surface)
Pressure at surface: 6.36 hPa / 0.00627 atmosphere
Surface temperature: max: 20C/293K/68F, min: -153C/120K/-243F.
Avg. surface temperature: -63C/-81F/210K/
One of the important themes in exploring Mars, has always been the search for life on this Planet.
Probabably, around the '80's or so, expectations slowly tempered somewhat. But, in the '50's, '60's, and '70's,
when space explorations started "to take off", it was quite a hot topic.
Expectations tempered in time, since it turned out, that Mars is not exactly a friendly Planet.
However, it could well be possible, that life existed in the distant past, and maybe still does (subterrain micro organisms?).
There are plenty of pointers that Mars, once used to be more friendly, and even had water, and a reasonable
atmosphere to potentially support life. However, long ago, unfortunate things happened to Mars.
We will see what Planetary scientists today, talk of the most probable causes, as to where it went wrong.
As we will see later on, even a couple of Moons of Jupiter and Saturn, might be considered as candidates
to host life. For example "Europa" (satelite of Jupiter), or "Enceladus" (satelite of Saturn) are likely to have
sub-surface Oceans, "at a reasonable" temperature (due to tidal induced heat).
Well, a number of Planetary scientists, at least, do not rule this out.
So, there indeed exists "some" chance for life to have developed at these moons.
I'am afraid we will have to wait for more research... I will definetely discuss those moons later in this note.
For about Mars, lots of thorough research already took place at many missions in the past, and more missions
are planned for the near future.
The total number of missions to Mars, from failed launches, to flyby's, to succesful orbit injections,
to succesful landings (including some sophisticated rovers), is large. Certainly well over 50.
The first landing on Mars, was with the Russian "Mars 3", which landed succesfully, but due to causes unknown,
failed after a dozen of seconds, or thereabout.
So, the first "intact" apparatus on the Surface of Mars, in 1971, was developed by the Sovjet Union.
Before that, several Mariner (US) and Mars missions (Sovjet Union) took place, but regrettably I have
to ignore all of those, otherwise this note will never end.... :-)...
But, when the Vikings came, it really was getting interesting !
4.2 The two Viking landers (succesfully touched the surface in 1976):
In 1976...Man, that was exciting, for older dudes like me. It really was. No joke here.
For the first time, 2 landers touched down, almost exclusively dedicated to find any trace of life.
The landers were each equipped with a laboratory, and a movable "sampler arm" (a spade, to say roughly),
was able to dig a sample of Martian soil, and to pour it into the laboratory.
One such Viking system, consisted of the Lander, and the Orbiter, where the orbiter had many tasks as well.
First, as a relay station between the Lander and Earth, and secondly, to make christal clear images
of the Martian Surface, and that succeeded extremely well too.
The landers were stationary in position (they were not rovers; they came later), but the clear pictures
of the local landscape, were astounding. Like a reddish Dune landscape, with scattered rocks, all over
the place, in all sizes.
Don't forget: these were the first ever images. Nobody really knew yet, how it all looked like.
Viking 1 (First color image)
Viking 1 (Sunset)
Viking 1 (Chryse Plains, "Big Joe")
Viking 1 (trenches created by sampler arm)
Viking 2 (Utopia Planitia)
Findings:
The orbiters collected much data. For one thing, they found geologic evidence of abundance of water in the past,
like outflow channels carved by floods, deltas, lakebeds etc.. This conclusion is almost unavoidable.
There is simply too much of findings to list here, in such a simple note.
But....now...
The big question: Did the Vikings found traces of life?:
Officialy, supported by *most* Planetary scientists: no conclusive evidence.
There were 4 experimental modules:
=> GCMS module:
The GCMS module measured no significant amount of organic molecules in the Martian soil.
It was certainly a high precision instrument. It was a bit of a surprise.
This should be a prerequisite for life. (*): See also the note below.
It should be noted, that the later Phoenix lander (2008), found "perchlorate" in Martian soil,
which, when samples gets heated, has the potential to destroy organic molecules.
Now, that is a fact, and indeed observed in several later tests. But to claim it as
the cause why the GCMS tests were negative, are likely to be labeled as "hypotheses".
There is thus, up to today, no conclusive statement about the outcomes of the GCMS experiments.
=> GEX module:
The GEX module tried to detect gasses, where a soil sample was "incubated" with nutritients.
(On Earth, all sorts of life forms would indeed "go" for those nutritients.)
The module then would try to detect various gasses which might be released, like Oxygen, Methane,
Nitrogen etc..
Amazingly, Oxygen dissapeared, and Carbondioxide started to appear.
However, the same occurred with a control sample, which was heated (disinfected) beforehand.
So, unfortunately, we might say that we actually have no result from the GEX experiments.
=> PR module:
The PR module, effectively tried to find if photosynthesis would take place.
With a soil sample, and an artificial atmosphere having Carbon monoxide, and Carbon dioxide,
using C14 instead of C12, it would be possible to see if new biomassa would have formed,
using the C14.
Note: C12 is the common isotope of Carbon, while C14 is much less common.
It seems from the available literature, that no positive results were obtained.
=> LR module:
The LR module, uses a sample of soil, and "incubates" it with nutritients.
Those nutritients used C14, instead of C12.
Would Carbon dioxide be produced, having the C14 isotope? Yes, it did !
Here, we have a positive result.
However, still there were some objections, which explains the observed effects using "Superoxide chemistry".
Sofar about a short description of the tests. I know that I must be extremely careful here.
Absolutely, I will not give any personal opinion here (which is obvious, ofcourse).
After studing quite a few articles, I have to say that, apart from a minority of Planetary scientists,
it seems that a consensus exists with Planetary scientists, for "no conclusive evidence".
The upcoming "Mars 2020" mission (planned July 2020), will do a renewed search for traces of life,
so that's gonna be very, very, exciting !
(*): According to most researchers in the field: One of the later rovers, Curiosity,
found organic molecules on Mars.
4.3 The Mars Rovers:
The Mars rovers. There are 4 of them in total, up to now.-Sojourner, landed on July 4, 1997.
-Spirit and Opportunity (the twins), landed on January 3 and January 24, 2004.
-Curiosity, landed on August 6, 2012.
Sojourner (1997), Spirit and Opportunity (2004), used the most Coolest Way, to do a touchdown on a Planet.
And Sojourner was the first to use this technology: bouncing balls Airbag technology.
Now..., Watch this:
Touch down of Spirit (YouTube clip).
Touch down of Sojourner (Pathfinder) (YouTube clip).
If you were amazed by the "airbag/bouncing ball" method, used by Sojourner, Spirit and Opportunity, then you may wonder
which tactic was applied with Curiosity Rover. You are not going the believe it, but a crane construction was used !
Touchdown of Curiosity (YouTube clip) (Nasa/JPL)
That one will be remembered by engineers, easily into the year 2520, and far beyond..
As presented in the animation above, was indeed how it went in reality.
Curiosity was a large and relatively heavy robot, which is why the "crane solution" was figured out.
Landed in 2012, the Curiosity rover is still operational (may 2020). One aspect of it's work are the high definition pictures
it took from the Martian landscape. Below, you see a brilliant example:
Curiosity: 1.8 billion pixel Panorama (taken end 2019)
Let's briefly zoom in to those machines, seperately.