There's quite a few things to think about here, so I'll make some categories.
Any scientific mission funded by government(s), which a mission of this magnitude would likely be heavily funded by multiple governments unless of course there is only one world government in the 2100s, requires a few set of prerequisite criteria which goes something like this:
1) A clear mission statement : Here's what we know and here is what we want to find out
2) A list of criteria which would define the minimum for success
3) A cost analysis
To tackle the first part, there's quite a few more details you'd want to think about in your prompt before thinking about the specialist you'd send on such a mission. First is this an attempt at first contact or not, is there a known alien civilization on this planet or not, have we made contact in the past or attempted to do so? 30 light years isn't very far on a astronomical scale so we would likely be able to tell whether there is an civilization living in this new solar system which is advanced enough to produce space craft capable of making it to the Oort cloud. The crew you'd send would be heavily dependent on all of the above factors. Since the last two parts of the three part criteria are all interconnected to the first part, I'll move on.
A data-collection mission
If the mission is about data collection, I'm going to have to disagree with the focus on specific scientists. Since data collection would be the objective, it is unlikely you'd want a bunch of specialized scientists. In previous missions, including the manned ones such as the Moon landings, the focus is on the technical expertise to complete the data collection itself, doing the actual science requires years and years of working with the data and is best done in the comfort of an office, not in situ. To further complicate this, presumably technology is better in the 2100s than it is today, since indicators of future technology point to highly advanced A.I. scientific specialists would become even less important. A.I. is great at recognizing patterns, sorting through, and quickly retrieving data, what it is not so great at (and with current technologies will never be great at) is being able to innovate to solve problems.
One of the presumptions for a data-collection mission (as opposed to making first contact) would be accessing the planet remotely. If the planet has a mass similar or larger than Earth, the easiest way to study it would be by taking images and spectral analysis from orbit, and only sending down probes for a closer look. Due to the difficulty in escaping the gravity of such a planet, it would not be advisable to land a craft capable of performing an interstellar journey. A lot of information can be gathered by orbiting a planet and observing the light reflected back from its surface. If specific features stand out, probes can be used to investigate these.
Planetary scientists and "image" scientists would be the the sort of specialist required for facilitating the data collection (I put image in quotes, not because it is not legitimate, it is, but because it is not very well known and will likely be called something different in the near future).
The main questions, if there is no intelligent aliens still there, is obviously why did the alien craft indicate this planet to be important. Why did they disappear, if they were there at all? If there is life, how advanced, and if there isn't life, was the planet ever capable of supporting life and if so, how long ago? These sort of questions can quite confidently be answered using the methods described above.
A first contact mission
This would be a whole nother game. Since there is no precedent for contacting alien life, the first question would be why wasn't it accomplished remotely. Presuming the long distance between Earth and this planet was the main culprit, the delegation for first contact would likely include looking for what kind of civilization this is, the level of hostility to expect and how to make contact in a non-threatening manner before considering, say, the biochemistry of the foliage on the planet.
The specialist for this mission would likely be staffing many more social scientists (sociologists and linguists), animal biologists and even possibly a few government officials before staffing biochemists and geologists.
Since there are so many ways this can go, there's not too much else that can be said without more information about what is already known about the planet and what is known about the alien craft.