Peer review is an essential aspect of publication in Icarus. The fundamental role of the reviewer is to provide advice to the Editor or Assistant Editors on the virtues, or lack thereof, of a manuscript submitted for publication. Typically it is the reviewers who will have the most direct and expert knowledge of the field addressed by the manuscript, so that the reviewer's advice is critical to the Editor's decision, not only in evaluating whether the manuscript should be accepted for publication but also in helping to make the manuscript as useful as possible to Icarus readers.

Matters that you might wish to address in your review of the manuscript include its scientific correctness and its originality, coverage of the relevant literature, its pertinence and significance to studies of our solar system or related investigations, as well as its conciseness. On all these issues, general impressions of the paper as well as specific advice to the author(s) will be helpful. On the question of the paper's brevity, suggestions as to particular sections that might be reduced or even eliminated would be most useful. Details on these and other useful aspects of your review are provided below.

In general, a given manuscript will be assigned to the Editor or to an Assistant Editor (AE), who in most cases will have the principal responsibility of identifying prospective reviewers on the basis of the authors' suggestions and his/her own knowledge of the relevant discipline. In general, each Icarus manuscript will have two reviewers, although occasionally a third (or even fourth) reviewer may be sought in cases of contentious topics or dichotomous reviewer advice.

You, the prospective reviewer, will first be asked to review the manuscript, either directly by the Editor or AE, or by the editorial office. Most commonly the request will be made by e-mail, but other forms of communication may also be used, as circumstances warrant. Before you are asked, the manuscript will be posted on the editorial office's website (see Section 1.2 below), where it is immediately accessible for your inspection using a username and password provided to you.

It should not take you long to decide whether or not you can do the review, so we ask for a prompt response to the request, the same day or the next business day if possible. If you need more time to reach a decision, please acknowledge the request promptly (so that we know you are not on travel and without e-mail for several weeks, for example), and let us know approximately when we can expect to hear from you. If you agree to do the review, please plan on completing it within three weeks for a regular submission, or two weeks for a Note (see Section 1.4 below).

In most cases the request will come by e-mail, which should also be the easiest way to respond. If it is more convenient, however, you may also respond by phone or fax.

All manuscripts will be posted on the editorial office's website, http://icarus.cornell.edu. To access a given manuscript, click Papers on the navigation bar at the top of the page. On this Manuscript Access page there will be a textbox into which you should enter the six-character manuscript number "Innnnn" for the manuscript you want to access (where "I" stands for "Icarus" and "nnnnn" is the five-digit manuscript number). You will then be asked for a username and password, both of which will have been supplied with the review request. Normally the username will be "r-Innnnn", where "nnnnn" is again the five-digit manuscript number, and the password will be a six-character string unique to reviewers of that manuscript.

You will be presented with a list of PDF files associated with that specific manuscript. There will always be a file for the whole manuscript, double-spaced. There will also be a file for title page and abstract only. You may access any or all of these files. If you have a very slow connection, you might want to access just the shorter title-and-abstract file if you can decide whether to do the review on that basis, and, if you agree to the review, access the full manuscript later.

Each item in the list of files is a link. When you click on it your browser will either attempt to open it or download it to your computer, depending on how the browser is set (often, a right-click will offer you the choice). Either way, you can examine the manuscript directly on your computer or print hardcopy if you wish.

Manuscript files are in PDF format. To open them you will need the Adobe Acrobat Reader, version 4.0 (earlier versions sometimes work, but sometimes don't). If you don't already have it, you can download the Reader version 4.0, for free, from the Adobe website (www.adobe.com).

If you lack internet access, the office will fax (or e-mail) you the title page and abstract in conjunction with the request for review and, if you agree to the review, send you (by post or by courier) hardcopy versions of the manuscript, this document (Information for Reviewers) and a review form (see Section 1.5).

Reviewers are reminded that manuscripts submitted to a scientific journal are confidential documents until they are published. The manuscript you are reviewing or are asked to review should be discussed only with the Editor or AE, or with editorial office staff. Your access to a manuscript under review is privileged; please do not disclose its content (or even title or authors) to any other individuals except with specific approval of the Editor, AE or the editorial office. If you decide not to review a manuscript that you have downloaded, we ask that you delete the PDF file(s) from your system.

Of all the factors that contribute to the length of the review and evaluation process, the greatest is usually the time a manuscript spends on a reviewer's desk, or in a reviewer's briefcase, waiting for him/her to get around to doing the review. We ask for your cooperation and rely on your good will in not prolonging this interval to no good end. The Golden Rule applies: It is not unlikely that the authors of the paper that you are presently reviewing will someday be reviewing one of your own papers; review as you would like to be reviewed.

The general guideline is that you should complete your review as promptly as is reasonable. More specifically, we ask that you complete your review within three weeks for a regular submission, and within two weeks for a Note, from the time you receive the manuscript. If specific circumstances warrant, this may be extended, but this should be uncommon and should be discussed beforehand with the Editor, AE or with editorial office staff. Please be realistic: If you anticipate that you cannot follow these timelines because of travel, teaching schedule, proposal deadlines, etc., don't agree to do the review in the first place. An editor would much rather hear a "No, I'm sorry" up front than to have to nag and cajole you three weeks later. If you promise to do a review and then fail to deliver, the likely result is that your review will be abandoned and the evaluation process will have to proceed without benefit of your review. This will delay the publication process and usually annoys all parties concerned.

Please submit your review on the editorial office website. Click the Submission button on the navigation bar, then, after you read the instructions on the resultant page, click the Review Submission link. You will be asked for manuscript number and then for username and password, just as for manuscript access; use the same username and password that allowed you access to the manuscript in the first place.

After entry of the correct username and password you will be presented with a "review form" page, which will include textboxes and scrollboxes. For each of several questions, please choose one of the scrollbox options provided; this is not the most important part of your review, but it provides a useful summary. One textbox is for your name, which will be disclosed to the Editor or AE but not to the authors (see Section 1.6). In the next textbox, labeled Comments for Authors, please enter whatever you have to say about this manuscript. These Comments will be transmitted directly to the authors, exactly as you type them. This is the most important part of the review. There is no checklist of points to cover; say whatever you think is important to say. You may type text directly into the textbox, or paste from another program. In the next textbox, labeled Comments for Editors, please enter specific comments just for "Editors eyes only". These Comments will NOT be transmitted to the authors.

Besides selecting options and entering text, you may wish to submit electronic files (figures, tables or text) as part of your review. The review page also provides a file upload facility, which works very much like the manuscript submission upload facility and which is also subject to similar restrictions on file type and length and on filename extensions. If you wish, you may write your remarks in a word processor and upload the word processor file rather than enter text in the Comments textbox. If you upload additional files, please indicate so in the review form, and clarify in the Comments to Editors whether or not these additional materials are meant for the authors or for the Editor only.

After you have entered text, selected scrollbox options, and perhaps specified files to upload, click the Proceed to Proof button at the bottom of the page. This will take you to a proofing page, from which you can either submit the review (the Submit Review button at the bottom) or return to the review form page (the Edit button) to make changes.

If you lack internet access and are working only with the hardcopy manuscript and hardcopy review form, please mail it or (preferably) fax it to the editorial office (607-255-6354).

Whether you submit your review via the website or otherwise, you might also want to return a hardcopy version of the manuscript with your handwritten annotations. If so, mail it to the Icarus editorial office at 413 Space Sciences Building, Cornell University, Ithaca, NY 14853-6801.

Neither the Editor, AE, nor the editorial office will disclose your identity to the authors. If you wish to "sign" your review and let the authors know who you are, put your name somewhere in the Comments to Authors box on either the website or the hardcopy review form.

Feel free to communicate informally directly with the Editor or AE, either at his/her instigation or yours. If the communication is in some black-and-white form (e-mail, fax, post), please copy it to the editorial office (icarus@astrosun.tn.cornell.edu). If by phone or in person, there is no need for a transcript, but it would be useful if there were some black- and-white allusion to the conversations. Your final, formal review, however, should still be submitted to the editorial office.

Peer review of a scientific manuscript is based on judgment, and application of evaluation criteria is typically quite subjective. Most experienced investigators usually have definite ideas about how to do a review, both in general as well as for Icarus in particular, and don't need to be told how to do it. A review of the guidelines is usually still instructive nonetheless. However, many young investigators or researchers working primarily outside of Planetary Science may not know how to structure a review in general or for Icarus in particular. While there is no exact formula, we hope that the following guidelines will be useful.

Despite the authors' best efforts, manuscripts are often not free of problems such as typographical errors, misspellings, minor (or major!) grammatical errors, incorrect figure or table citations, missing or superfluous references, etc. Reviewers are encouraged to point these out, as doing so is a service to authors, editors and readers.

In rare occasions, the frequency of such mechanical errors rises to a level at which it is both an annoyance to the reviewer and a distraction from the scientific message. If you consider that this is the case, or more generally that the authors have been careless or negligent in preparing the manuscript, don't do a scientific review, just state your opinion that the manuscript is "unfit for review". This should be automatic if the manuscript has a missing figure or table.

Irrespective of intrinsic scientific merit, a manuscript is not suitable for publication in Icarus if its subject lies outside the journal's scope. If it is your judgment that the manuscript in question is inappropriate for Icarus because it's outside that scope, then you can just say that without reviewing the science.

You can look up Icarus's statement of scope if you like (in Information for Authors, Section 1.1), but it's not a complicated statement. The scope of Icarus is observational, experimental, or theoretical research concerning the astronomy, geology, meteorology, physics, chemistry, biology, and other scientific aspects of our Solar System or extrasolar systems. In most cases there will be no ambiguity about whether a given manuscript is within the journal's scope. In marginal cases about which you may be unsure, say that it's marginal and/or that you're not sure about it. You should also feel free to discuss appropriateness with the AE or with the Editor. In a very real sense, the definition of just what constitutes "Solar System studies" is in the perception of the scientific community that practices these arts and answers to those names, so your opinion on this issue is important.

In evaluating a manuscript you should also consider its significance and its relevance to the Icarus readership and to the scientific community at large. For example, many manuscripts focus on detailed, methodical, and sometimes necessarily esoteric measurements of objects or phenomena and may include exquisite analytical work, a thorough description of experimental procedures and an honest discussion of results. However, unless there's a strong tie-in to specific issues in solar system studies or a broader discussion of the general relevance of the work towards important questions in planetary science, the work may be neither very significant nor very interesting to readers, and it should not be published in Icarus. Again, this is a subjective call, but it is the reviewer's responsibility to "call it as they see it" for the benefit of the Editor's ultimate decision. If there is any question about the broader relevance and significance of a very narrow or local study, it it the authors' responsibility to make the connection, not the reviewer's.

There are several more-or-less objective criteria involved in manuscript evaluation, as described below. In your review it is not necessary to check off each one; typically reviewers will mention these various aspects only when something is wrong with them. This is not inappropriate; sometimes an identified flaw will prove fatal, but more often remediation of a flaw helps improve the paper.

Foremost is the issue of whether the authors have made some substantive scientific mistake (in the reviewer's opinion, anyway). Perhaps the data, or their error bars, are suspect. Perhaps the authors have made some mathematical mistake in data reduction or in derivation. Perhaps figures are misplotted. Often enough, if more subjectively, you may consider that there is something wrong with how the authors proceed from premises and observations to conclusions and generalizations. In most cases it will have little effect to ask that the authors change their conclusions to alternative interpretations more favored by the reviewer, and rightly so, since it is the authors' names on the paper, not the reviewer's. But it is certainly appropriate to ask that the authors fill in intermediate steps in their reasoning and/or that they at least mention alternative interpretations.

Reviewers should also consider whether the work is original, and/or whether the authors may have reported substantially the same thing elsewhere (exclusive of abstracts or other "gray" literature). A related question is whether the authors have cited and given credit to relevant antecedent work by others. Priority disputes are usually ugly and distasteful, and it is better to avoid them at the outset by calling attention to any perceived deficiency in giving credit where credit is due.

There is no arbitrary preset limit on the length of an Icarus paper, but that doesn't mean you should ignore length. If you think a manuscript is too long, in terms of tables and/or figures as well as text, and can be shortened without serious damage to the message, please say so. The issue is not just saving trees. Everybody's busy and, other things being equal, more people will read a short paper than a long one, and you will serve readers well if you help minimize dilution of the science by unnecessary figures, tables and/or verbiage. But don't just object to length as a matter of principle: Specifically indicate which figures or tables can be dispensed with, or where text should be trimmed or eliminated.

The converse also applies. If you consider that science will be served by adding tables or figures, or adding prose to describe methods, reasoning, implications, etc., say that as well.

Reviewers sometimes seem to think that their job is to identify what's wrong with a manuscript and tell the authors to fix it. That's true, but it's only part of the story, Even if there's nothing wrong with a manuscript, or if whatever's wrong can be fixed, that doesn't mean it should be published in Icarus. To warrant publication, there has to be something right with it too. The work should be of high scientific quality, it should be original, it should constitute a significant contribution to scientific understanding, and it should be something that the readership will be (or should be) interested in (see Section 2.3). Just how high the bar should be is a matter of judgement and is impossible to define in general terms; this is another respect in which reviewers' advice to the Editors helps to determine the nature of the journal and the state of the art.

So please don't confine your review to identifying what's wrong with the manuscript. If your opinion is that the manuscript warrants publication, say why - say what's right with it.

Sometimes a review discusses many aspects of a manuscript without providing a clear bottom line. Make sure the Assistant Editor or the Editor know whether you think the manuscript should be accepted or rejected or re-evaluated after certain changes are made. Even when you think the intrinsic scientific merit of the manuscript warrants publication, you may make several recommendations for changes; if so, make it clear which are just constructive suggestions that the authors may or may not adopt, at their discretion, and which you think are necessary before the manuscript is suitable for publication. In general, the reviewer's principal function is to provide expert advice, so you should make it explicitly clear just what your advice is.

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