There were three things in particular about which I persistently sought the reasons why they were such and not otherwise: the number, the size, and the motion of the circles. ...  In the beginning I attacked the business by numbers, and considered whether one circle was twice another, or three times, or four times, or whatever, and how far any one was separated from another according to Copernicus.  I wasted a great deal of time on that toil, as if at a game, since no agreement appeared either in the proportions themselves or in the differences; and I derived nothing of value from that except that I engraved deeply on my memory the distances which were published by Copernicus. ...  If (thought I) God allotted motions to the spheres to correspond with their distances, similarly he made the distances themselves correspond with something. Since, then, this method was not a success, I tried an approach by another way, of remarkable boldness.  Between Jupiter and Mars I placed a new planet, and also another between Venus and Mercury, which were to be invisible perhaps on account of their tiny size, and I assigned periodic times to them.  For I thought that in this way I should produce some agreement between the ratios. ...  Yet the interposition of a single planet was not sufficient for the huge gap between Jupiter and Mars; for the ratio of Jupiter to the new planet remained greater than that of Saturn to Jupiter.

Mercury   Venus   Earth   Mars   Jupiter   Saturn
  32       59      81     123      424      777

And who knows whether or not there are missing planets which have moved out of the wide space which exists between Mars and Jupiter.

... supposing the distance of the earth from the Sun to be divided into ten equal parts, of these the distance of Mercury will be about four, of Venus seven, of Mars fifteen, of Jupiter fifty-two, and that of Saturn ninety-five.

Not only has it been reserved for modern astronomers to enrich our sky with new planets, but also to push back the frontiers of our planetary system.

Take notice of the distance of the planets from one another, and recognise that almost all are separated from one another in a proportion which matches their bodily magnitudes. Divide the distance of the Sun to Saturn into 100 parts: then Mercury is separated by 4 such parts from the Sun, Venus by 4 + 3 = 7 such parts, the Earth by 4 + 6 = 10, Mars 4 + 12 = 16. But notice that from Mars to Jupiter there comes a deviation from this so-exact progression. From Mars there follows a space of 4 + 24 = 28 such parts, but so far no planet or satellite was sighted there. But should the Lord Architect have left that space empty? Not at all. Let us therefore assume that this space without doubt belongs to the still-undiscovered satellites of Mars; let us also add that perhaps Jupiter still has around itself some smaller ones which have not been sighted yet by any telescope. Next to this still-unexplored space there rises Jupiter's sphere of influence at 4 + 48 = 52 parts; and that of Saturn at 4 + 96 = 100 parts. What a wonderful relation!

This latter point seems in particular to follow from the astonishing relation which the known six planets observe in their distances from the Sun. Let the distance from the Sun to Saturn be taken as 100, then Mercury is separated by 4 such parts from the Sun. Venus is 4 + 3 = 7. The Earth 4 + 6 = 10. Mars 4 + 12 = 16. Now comes a gap in this so orderly progression. After Mars there follows a space of 4 + 24 = 28 parts, in which no planet has yet been seen. Can one believe that the Founder of the universe had left this space empty? Certainly not. From here we come to the distance of Jupiter by 4 + 48 = 52 parts, and finally to that of Saturn by 4 + 96 = 100 parts.

Your noticing on page 462 of your book of the distances of the planets would have pleased Kepler, who wrote an entire book on this question; it could lend a reason as to why the planets are distant from the Sun according to a particular and simple law unrelated to their mass.

That this chief planet between Mars and Jupiter must complete its revolution around the Sun in $4\large\frac{1}{2}\normalsize$ years can be computed from a law discovered by Kepler, namely that the squares of the orbital periods of two planets are to one another as are the cubes of their distances from the Sun.

Most people are aware that the celebrated astronomer Piazzi discovered the small planet Ceres at Palermo in this very observatory, with an instrument of Ramsden's which we had the satisfaction of seeing. It was made on the 1st of January, 1801, at which period the present astronomer, Cacciatore, was Piazzi's assistant in the observatory of which he is now the chief. As Piazzi was at that time engaged in making the noble catalogue of the stars, which has since become so well known, he placed himself at the telescope, and observed the stars as they passed the meridian, while Cacciatore wrote down the times, and the polar distances, as they were read off by his chief. Certain stars passed the wires, and were recorded as usual on the 1st of January, 1801. On the next night, when the same part of the heavens came under review, several of the stars observed the evening before were again looked at, and their places recorded. Of these, however, there was one which did not fit the position assigned to it on the previous night, either in right ascension, or in declination. "I think," said Piazzi to his companion, "you must, accidentally, have written down the time of that star's passage, and its distance from the pole, incorrectly." "To this," said Cacciatore, who told me the story, "I made no reply, but took especial pains to set down the next evening's observations with great care. On the third night there again occurred a discordance, and again a remark from Piazzi that an erroneous entry had probably been made by me of the place of the star. I was rather piqued at this," said Cacciatore, "and respectfully suggested that possibly the error lay in the observation, not in the record. Under these circumstances, and both parties being fully awakened as to the importance of the result, we watched for the transit of the disputed star with great anxiety on the fourth night. When lo, and behold! it was again wide of the place it had occupied in the heavens on the preceding and all the other nights on which it had been observed. 'Oh, oh!' cried the delighted Piazzi, 'we have found a planet while we thought we were observing a fixed star; let us watch it more attentively?'" The result soon confirmed this conjecture, and thus was made one of the most interesting, and I may say useful, astronomical discoveries of modern times.

Sicily - Palermo, January 15. On the 1st of this month, a new comet in the shoulder of Taurus, near the 19th star of Mayer, was discovered from our observatory. It was observed on 1st, 2nd, 3rd and 4th, as it passed the meridian. Although it is not covered with any kind of nebulous spot, it still cannot be seen with the naked eye. Its movement is retrograde; it goes forward towards the north.

I have announced this star as a comet, but since it shows no nebulosity, and moreover, since it had a slow and rather uniform motion, I surmise that it could be something better than a comet. However, I would not by any means advance publicly this conjecture. As soon as I shall have a larger number of observations, I will try to compute its elements.

If the Germans think they have the right to name somebody else's discoveries they can call my new star the way they want: as for me I will always call it Ceres and I will be very obliged if you and your colleagues will do the same.

The Greek name Hera is preferred to the Latin name Juno, because 1) the latter has already been ascribed to the planet Venus; 2) Hera is the name of a city in Sicily, through which the memory of the discoveries made on this island and the glorious name of the discoverer of this eighth primary planet will be contained and immortalised.

I have noted in your journal the desire of a few to give this new planet the name Juno rather than Ceres. I trust that these astronomers, who are peaceful people, will never consent to having their deities called the name of a goddess as anxious, jealous and vindictive as Juno. Jupiter finally chased her from the sky; in her place he had Ceres appear, who has so much more right to the homage of mankind.

What is going on with the Ceres Ferdinandea? Nothing has been found as yet either in France or in Germany. Peoples are starting to doubt: Already sceptics are making jokes about it. What is Devil Piazzi doing? Lalande wrote me that Piazzi has changed again his observations and that he has made a new Edition of them! What does that mean? Lalande in his letter adds: "This is why I do not believe in the planet."

... it seems somewhat strange that the general problem, - "To determine the orbit of a heavenly body, without any hypothetical assumption, from observations not embracing a great period of time, and not allowing a selection with a view to the application of special methods," was almost wholly neglected up to the beginning of the present century; or, at least, not treated by any one in a manner worthy of its importance; since it assuredly commended itself to mathematicians by its difficulty and elegance, even if its great utility in practice were not apparent. An opinion had universally prevailed that a complete determination from observations embracing a short interval of time was impossible, - an ill-founded opinion, - for it is now clearly shown that the orbit of a heavenly body may be determined quite nearly from good observations embracing only a few days; and this without any hypothetical assumption.

Some ideas occurred to me in the month of September of the year 1801, engaged at the time on a very different subject, which seemed to point to the solution of the great problem of which I have spoken. Under such circumstances we not infrequently, for fear of being too much led away by an attractive investigation, suffer the associations of ideas, which, more attentively considered, might have proved most fruitful in results, to be lost from neglect. And the same fate might have befallen these conceptions, had they not happily occurred at the most propitious moment for their preservation and encouragement that could have been selected. For just about this time the report of the new planet, discovered on the first day of January of that year with the telescope at Palermo, was the subject of universal conversation; and soon afterwards the observations made by that distinguished astronomer Piazzi from the above date to the eleventh of February were published. Nowhere in the annals of astronomy do we meet with so great an opportunity, and a greater one could hardly be imagined, for showing most strikingly, the value of this problem, than in this crisis and urgent necessity, when all hope of discovering in the heavens this planetary atom, among innumerable small stars after the lapse of nearly a year, rested solely upon a sufficiently approximate knowledge of its orbit to be based upon these very few observations. Could I ever have found a more seasonable opportunity to test the practical value of my conceptions, than now in employing them for the determination of the orbit of the planet Ceres, which during these forty-one days had described a geocentric arc of only three degrees, and after the lapse of a year must be looked for in a region of the heavens very remote from that in which it was last seen? This first application of the method was made in the month of October, 1801, and the first clear night, when the planet was sought for [by von Zach on 7 December 1801] as directed by the numbers deduced from it, restored the fugitive to observation.

Gauss's first goal, and the most challenging one, was to determine the distance of Ceres from the Earth, for at least one of the three observations. In fact, Gauss chose the second of the unknown distances - the one corresponding to the intermediate of the three selected observations - as the prime target of his efforts. Finding that distance essentially  breaks the back of the problem. Having accomplished that, Gauss would be in a position to successively "mop up" the rest. In fact, Gauss used his calculation of that value to determine the distances for the first and third observations; from that, in turn, he determined the corresponding spatial positions of Ceres, and from the two spatial conditions and the corresponding time, he calculated a first approximation of the orbital elements. Using the coherence provided by that approximate orbital calculation, he could revise the initial calculation of the distances, and obtain a second, more precise orbit, and so on, until all values in the calculation became coherent with each other and the three selected observations.

Now as we already have Planets, Comets, Satellites, pray help me to another dignified name as soon as possible. If I could in any way express the condition of a nimble, small, interloper going obliquely through the majestic orbits of the great bodies of the Solar System it would be just what is required.

These new stars are mixed with the small fixed stars of the heavens and resemble them so much that even with a good telescope they cannot be distinguished from them. From this their asteroidal or starlike appearance I take my name, and call these new celestial bodies Asteroids.

Moreover, if we were to call Ceres a planet, it would not fill the intermediate space between Mars and Jupiter with the proper dignity required for that station. Whereas, in the rank of Asteroids it stands first, and on account of the novelty of the discovery reflects double honour on the present age as well as on Mr Piazzi who discovered it. I hope you will see the above classification in its proper light, as so far from undervaluing your eminent discovery it places it, in my opinion, in a more exalted station. To be the first who made us acquainted with a new species of primary heavenly bodies is certainly more meritorious than merely to add what, if it were called planet, must stand in a very inferior situation of smallness.

Dawn discovered that the inner solar system's only dwarf planet was an ocean world where water and ammonia reacted with silicate rocks. As the ocean froze, salts and other tell-tale minerals concentrated into deposits that are now exposed in many locations across the surface. Dawn also found organics in several locations on Ceres' surface.